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 $19.48   8.244%   $21.0859   $21.09   $21.10   $21.10  
  Purchase #2 $204.33   8.568%   $221.837   $221.84   $221.85   $221.80  
  Purchase #3 $187.35   11.789%   $209.4367   $209.44   $209.45   $209.40  
  Purchase #4 $229.54   7.290%   $246.2735   $246.27   $246.25   $246.30  
  Purchase #5 $200.53   8.228%   $217.0296   $217.03   $217.05   $217.00  
  Purchase #6 $202.48   6.221%   $215.0763   $215.08   $215.10   $215.10  
  Purchase #7 $133.87   9.383%   $146.431   $146.43   $146.45   $146.40  
  7 purchase totals = $1,177.58       $1,277.1700   $1,277.18   $1,277.25   $1,277.10