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 $212.49   10.599%   $235.0118   $235.01   $235.00   $235.00  
  Purchase #2 $64.28   11.117%   $71.426   $71.43   $71.45   $71.40  
  Purchase #3 $117.66   3.622%   $121.9216   $121.92   $121.90   $121.90  
  Purchase #4 $202.64   13.868%   $230.7421   $230.74   $230.75   $230.70  
  Purchase #5 $249.97   12.442%   $281.0713   $281.07   $281.05   $281.10  
  Purchase #6 $80.29   9.758%   $88.1247   $88.12   $88.10   $88.10  
  Purchase #7 $208.63   4.264%   $217.526   $217.53   $217.55   $217.50  
  7 purchase totals = $1,135.96       $1,245.8235   $1,245.82   $1,245.80   $1,245.70