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 $170.60   13.738%   $194.037   $194.04   $194.05   $194.00  
  Purchase #2 $24.67   4.412%   $25.7584   $25.76   $25.75   $25.80  
  Purchase #3 $56.33   12.758%   $63.5166   $63.52   $63.50   $63.50  
  Purchase #4 $182.83   3.783%   $189.7465   $189.75   $189.75   $189.70  
  Purchase #5 $95.59   3.413%   $98.8525   $98.85   $98.85   $98.90  
  Purchase #6 $14.47   12.581%   $16.2905   $16.29   $16.30   $16.30  
  Purchase #7 $202.45   11.593%   $225.92   $225.92   $225.90   $225.90  
  7 purchase totals = $746.94       $814.1215   $814.13   $814.10   $814.10