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 $245.67   9.266%   $268.4338   $268.43   $268.45   $268.40  
  Purchase #2 $28.57   13.655%   $32.4712   $32.47   $32.45   $32.50  
  Purchase #3 $18.37   13.754%   $20.8966   $20.90   $20.90   $20.90  
  Purchase #4 $110.59   4.429%   $115.488   $115.49   $115.50   $115.50  
  Purchase #5 $247.51   10.786%   $274.2064   $274.21   $274.20   $274.20  
  Purchase #6 $87.32   5.371%   $92.01   $92.01   $92.00   $92.00  
  Purchase #7 $46.56   6.860%   $49.754   $49.75   $49.75   $49.80  
  7 purchase totals = $784.59       $853.2600   $853.26   $853.25   $853.30