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 $66.77   3.206%   $68.9106   $68.91   $68.90   $68.90  
  Purchase #2 $134.76   11.121%   $149.7467   $149.75   $149.75   $149.70  
  Purchase #3 $115.51   12.594%   $130.0573   $130.06   $130.05   $130.10  
  Purchase #4 $174.91   11.831%   $195.6036   $195.60   $195.60   $195.60  
  Purchase #5 $244.66   7.301%   $262.5226   $262.52   $262.50   $262.50  
  Purchase #6 $92.35   4.368%   $96.3838   $96.38   $96.40   $96.40  
  Purchase #7 $48.64   4.634%   $50.894   $50.89   $50.90   $50.90  
  7 purchase totals = $877.60       $954.1186   $954.11   $954.10   $954.10