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 $23.56   5.739%   $24.9121   $24.91   $24.90   $24.90  
  Purchase #2 $160.76   9.107%   $175.4004   $175.40   $175.40   $175.40  
  Purchase #3 $158.87   9.473%   $173.9198   $173.92   $173.90   $173.90  
  Purchase #4 $119.68   11.317%   $133.2242   $133.22   $133.20   $133.20  
  Purchase #5 $127.95   6.276%   $135.9801   $135.98   $136.00   $136.00  
  Purchase #6 $156.49   11.683%   $174.7727   $174.77   $174.75   $174.80  
  Purchase #7 $60.35   11.317%   $67.1798   $67.18   $67.20   $67.20  
  7 purchase totals = $807.66       $885.3891   $885.38   $885.35   $885.40