Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $211.66   4.478%   $221.1381   $221.14   $221.15   $221.10  
  Purchase #2 $175.66   11.235%   $195.3954   $195.40   $195.40   $195.40  
  Purchase #3 $217.45   5.457%   $229.3162   $229.32   $229.30   $229.30  
  Purchase #4 $243.37   13.410%   $276.0059   $276.01   $276.00   $276.00  
  Purchase #5 $110.42   12.233%   $123.9277   $123.93   $123.95   $123.90  
  Purchase #6 $232.80   7.421%   $250.0761   $250.08   $250.10   $250.10  
  Purchase #7 $161.39   6.306%   $171.5673   $171.57   $171.55   $171.60  
  7 purchase totals = $1,352.75       $1,467.4267   $1,467.45   $1,467.45   $1,467.40