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 $185.92   4.488%   $194.2641   $194.26   $194.25   $194.30  
  Purchase #2 $25.38   3.155%   $26.1807   $26.18   $26.20   $26.20  
  Purchase #3 $68.81   6.417%   $73.2255   $73.23   $73.25   $73.20  
  Purchase #4 $54.59   11.137%   $60.6697   $60.67   $60.65   $60.70  
  Purchase #5 $123.75   10.709%   $137.0024   $137.00   $137.00   $137.00  
  Purchase #6 $143.29   11.237%   $159.3915   $159.39   $159.40   $159.40  
  Purchase #7 $85.34   13.413%   $96.7867   $96.79   $96.80   $96.80  
  7 purchase totals = $687.08       $747.5206   $747.52   $747.55   $747.60