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 $230.49   8.357%   $249.752   $249.75   $249.75   $249.80  
  Purchase #2 $58.99   3.739%   $61.1956   $61.20   $61.20   $61.20  
  Purchase #3 $199.31   3.850%   $206.9834   $206.98   $207.00   $207.00  
  Purchase #4 $32.94   6.860%   $35.1997   $35.20   $35.20   $35.20  
  Purchase #5 $126.94   5.330%   $133.7059   $133.71   $133.70   $133.70  
  Purchase #6 $65.72   11.240%   $73.1069   $73.11   $73.10   $73.10  
  Purchase #7 $247.34   4.310%   $258.0004   $258.00   $258.00   $258.00  
  7 purchase totals = $961.73       $1,017.9439   $1,017.95   $1,017.95   $1,018.00