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 $160.35   13.470%   $181.9491   $181.95   $181.95   $181.90  
  Purchase #2 $159.63   4.710%   $167.1486   $167.15   $167.15   $167.10  
  Purchase #3 $220.72   4.172%   $229.9284   $229.93   $229.95   $229.90  
  Purchase #4 $195.58   6.244%   $207.792   $207.79   $207.80   $207.80  
  Purchase #5 $92.75   10.357%   $102.3561   $102.36   $102.35   $102.40  
  Purchase #6 $147.66   12.436%   $166.023   $166.02   $166.00   $166.00  
  Purchase #7 $163.51   4.351%   $170.6243   $170.62   $170.60   $170.60  
  7 purchase totals = $1,140.20       $1,225.8215   $1,225.82   $1,225.80   $1,225.70