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 $195.65   8.235%   $211.7618   $211.76   $211.75   $211.80  
  Purchase #2 $62.77   3.829%   $65.1735   $65.17   $65.15   $65.20  
  Purchase #3 $206.46   11.172%   $229.5257   $229.53   $229.55   $229.50  
  Purchase #4 $148.90   6.622%   $158.7602   $158.76   $158.75   $158.80  
  Purchase #5 $122.62   8.342%   $132.849   $132.85   $132.85   $132.80  
  Purchase #6 $237.92   11.153%   $264.4552   $264.46   $264.45   $264.50  
  Purchase #7 $159.87   13.795%   $181.9241   $181.92   $181.90   $181.90  
  7 purchase totals = $1,134.19       $1,244.4495   $1,244.45   $1,244.40   $1,244.50