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 $168.83   11.254%   $187.8301   $187.83   $187.85   $187.80  
  Purchase #2 $190.91   11.192%   $212.2766   $212.28   $212.30   $212.30  
  Purchase #3 $244.29   12.567%   $274.9899   $274.99   $275.00   $275.00  
  Purchase #4 $33.48   12.644%   $37.7132   $37.71   $37.70   $37.70  
  Purchase #5 $226.38   13.141%   $256.1286   $256.13   $256.15   $256.10  
  Purchase #6 $133.75   11.795%   $149.5258   $149.53   $149.55   $149.50  
  Purchase #7 $206.63   11.207%   $229.787   $229.79   $229.80   $229.80  
  7 purchase totals = $1,204.27       $1,348.2512   $1,348.26   $1,348.35   $1,348.20