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 $222.62   6.248%   $236.5293   $236.53   $236.55   $236.50  
  Purchase #2 $208.98   8.299%   $226.3233   $226.32   $226.30   $226.30  
  Purchase #3 $71.74   7.485%   $77.1097   $77.11   $77.10   $77.10  
  Purchase #4 $62.43   3.565%   $64.6556   $64.66   $64.65   $64.70  
  Purchase #5 $146.54   8.647%   $159.2113   $159.21   $159.20   $159.20  
  Purchase #6 $152.25   12.360%   $171.0681   $171.07   $171.05   $171.10  
  Purchase #7 $30.78   4.226%   $32.0808   $32.08   $32.10   $32.10  
  7 purchase totals = $895.34       $966.9781   $966.98   $966.95   $967.00