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 $32.84   13.491%   $37.2704   $37.27   $37.25   $37.30  
  Purchase #2 $125.27   8.386%   $135.7751   $135.78   $135.80   $135.80  
  Purchase #3 $84.35   8.352%   $91.3949   $91.39   $91.40   $91.40  
  Purchase #4 $205.56   9.570%   $225.2321   $225.23   $225.25   $225.20  
  Purchase #5 $71.57   13.358%   $81.1303   $81.13   $81.15   $81.10  
  Purchase #6 $78.52   5.252%   $82.6439   $82.64   $82.65   $82.60  
  Purchase #7 $216.55   12.858%   $244.394   $244.39   $244.40   $244.40  
  7 purchase totals = $814.66       $897.8407   $897.83   $897.90   $897.80