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 $195.94   12.290%   $220.021   $220.02   $220.00   $220.00  
  Purchase #2 $73.52   13.154%   $83.1908   $83.19   $83.20   $83.20  
  Purchase #3 $182.76   6.111%   $193.9285   $193.93   $193.95   $193.90  
  Purchase #4 $246.60   3.692%   $255.7045   $255.70   $255.70   $255.70  
  Purchase #5 $112.90   8.467%   $122.4592   $122.46   $122.45   $122.50  
  Purchase #6 $76.80   11.871%   $85.9169   $85.92   $85.90   $85.90  
  Purchase #7 $45.65   11.742%   $51.0102   $51.01   $51.00   $51.00  
  7 purchase totals = $934.17       $1,012.2311   $1,012.23   $1,012.20   $1,012.20