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 $58.83   6.516%   $62.6634   $62.66   $62.65   $62.70  
  Purchase #2 $234.63   3.459%   $242.7459   $242.75   $242.75   $242.70  
  Purchase #3 $94.91   4.364%   $99.0519   $99.05   $99.05   $99.10  
  Purchase #4 $237.67   8.599%   $258.1072   $258.11   $258.10   $258.10  
  Purchase #5 $106.74   10.816%   $118.285   $118.29   $118.30   $118.30  
  Purchase #6 $59.73   4.600%   $62.4776   $62.48   $62.50   $62.50  
  Purchase #7 $18.60   9.287%   $20.3274   $20.33   $20.35   $20.30  
  7 purchase totals = $811.11       $863.6584   $863.67   $863.70   $863.70