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 $61.82   13.817%   $70.3617   $70.36   $70.35   $70.40  
  Purchase #2 $208.43   6.404%   $221.7779   $221.78   $221.80   $221.80  
  Purchase #3 $160.74   12.442%   $180.7393   $180.74   $180.75   $180.70  
  Purchase #4 $205.63   8.693%   $223.5054   $223.51   $223.50   $223.50  
  Purchase #5 $235.38   6.607%   $250.9316   $250.93   $250.95   $250.90  
  Purchase #6 $219.61   7.446%   $235.9622   $235.96   $235.95   $236.00  
  Purchase #7 $56.92   12.245%   $63.8899   $63.89   $63.90   $63.90  
  7 purchase totals = $1,148.53       $1,247.1680   $1,247.17   $1,247.20   $1,247.20