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 $203.94   8.485%   $221.2443   $221.24   $221.25   $221.20  
  Purchase #2 $158.99   10.351%   $175.4471   $175.45   $175.45   $175.40  
  Purchase #3 $77.97   8.391%   $84.5125   $84.51   $84.50   $84.50  
  Purchase #4 $198.69   5.266%   $209.153   $209.15   $209.15   $209.20  
  Purchase #5 $194.75   5.219%   $204.914   $204.91   $204.90   $204.90  
  Purchase #6 $126.71   7.560%   $136.2893   $136.29   $136.30   $136.30  
  Purchase #7 $201.61   5.546%   $212.7913   $212.79   $212.80   $212.80  
  7 purchase totals = $1,162.66       $1,244.3515   $1,244.34   $1,244.35   $1,244.30