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 $60.91   8.127%   $65.8602   $65.86   $65.85   $65.90  
  Purchase #2 $64.58   10.151%   $71.1355   $71.14   $71.15   $71.10  
  Purchase #3 $219.45   11.322%   $244.2961   $244.30   $244.30   $244.30  
  Purchase #4 $133.88   3.567%   $138.6555   $138.66   $138.65   $138.70  
  Purchase #5 $69.91   7.192%   $74.9379   $74.94   $74.95   $74.90  
  Purchase #6 $60.75   10.371%   $67.0504   $67.05   $67.05   $67.10  
  Purchase #7 $151.82   5.273%   $159.8255   $159.83   $159.85   $159.80  
  7 purchase totals = $761.30       $821.7611   $821.78   $821.80   $821.80