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 $92.78   13.185%   $105.013   $105.01   $105.00   $105.00  
  Purchase #2 $136.70   3.373%   $141.3109   $141.31   $141.30   $141.30  
  Purchase #3 $71.26   5.494%   $75.175   $75.18   $75.20   $75.20  
  Purchase #4 $190.73   6.423%   $202.9806   $202.98   $203.00   $203.00  
  Purchase #5 $209.33   9.444%   $229.0991   $229.10   $229.10   $229.10  
  Purchase #6 $132.36   10.704%   $146.5278   $146.53   $146.55   $146.50  
  Purchase #7 $119.85   11.590%   $133.7406   $133.74   $133.75   $133.70  
  7 purchase totals = $953.01       $1,033.8470   $1,033.85   $1,033.90   $1,033.80