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 $34.94   7.597%   $37.5944   $37.59   $37.60   $37.60  
  Purchase #2 $49.90   10.256%   $55.0177   $55.02   $55.00   $55.00  
  Purchase #3 $220.34   3.741%   $228.5829   $228.58   $228.60   $228.60  
  Purchase #4 $169.98   7.147%   $182.1285   $182.13   $182.15   $182.10  
  Purchase #5 $34.84   13.455%   $39.5277   $39.53   $39.55   $39.50  
  Purchase #6 $240.52   11.207%   $267.4751   $267.48   $267.50   $267.50  
  Purchase #7 $64.33   8.546%   $69.8276   $69.83   $69.85   $69.80  
  7 purchase totals = $814.85       $880.1539   $880.16   $880.25   $880.10