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 $67.92   13.233%   $76.9079   $76.91   $76.90   $76.90  
  Purchase #2 $165.60   6.709%   $176.7101   $176.71   $176.70   $176.70  
  Purchase #3 $87.35   3.390%   $90.3112   $90.31   $90.30   $90.30  
  Purchase #4 $224.63   5.615%   $237.243   $237.24   $237.25   $237.20  
  Purchase #5 $162.39   5.478%   $171.2857   $171.29   $171.30   $171.30  
  Purchase #6 $25.72   5.816%   $27.2159   $27.22   $27.20   $27.20  
  Purchase #7 $61.46   12.693%   $69.2611   $69.26   $69.25   $69.30  
  7 purchase totals = $795.07       $848.9349   $848.94   $848.90   $848.90