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 $182.48   13.260%   $206.6768   $206.68   $206.70   $206.70  
  Purchase #2 $158.41   8.324%   $171.596   $171.60   $171.60   $171.60  
  Purchase #3 $94.80   9.768%   $104.0601   $104.06   $104.05   $104.10  
  Purchase #4 $66.65   6.497%   $70.9803   $70.98   $71.00   $71.00  
  Purchase #5 $150.43   12.110%   $168.6471   $168.65   $168.65   $168.60  
  Purchase #6 $68.80   13.566%   $78.1334   $78.13   $78.15   $78.10  
  Purchase #7 $102.94   9.114%   $112.322   $112.32   $112.30   $112.30  
  7 purchase totals = $824.51       $912.4157   $912.42   $912.45   $912.40