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 $55.58   12.110%   $62.3107   $62.31   $62.30   $62.30  
  Purchase #2 $207.27   11.693%   $231.5061   $231.51   $231.50   $231.50  
  Purchase #3 $129.52   5.116%   $136.1462   $136.15   $136.15   $136.10  
  Purchase #4 $31.94   11.873%   $35.7322   $35.73   $35.75   $35.70  
  Purchase #5 $247.45   7.206%   $265.2812   $265.28   $265.30   $265.30  
  Purchase #6 $101.38   9.783%   $111.298   $111.30   $111.30   $111.30  
  Purchase #7 $54.41   9.555%   $59.6089   $59.61   $59.60   $59.60  
  7 purchase totals = $827.55       $901.8833   $901.89   $901.90   $901.80