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 $24.95   11.399%   $27.7941   $27.79   $27.80   $27.80  
  Purchase #2 $231.48   12.501%   $260.4173   $260.42   $260.40   $260.40  
  Purchase #3 $228.84   5.291%   $240.9479   $240.95   $240.95   $240.90  
  Purchase #4 $58.68   3.494%   $60.7303   $60.73   $60.75   $60.70  
  Purchase #5 $17.33   10.642%   $19.1743   $19.17   $19.15   $19.20  
  Purchase #6 $162.56   12.827%   $183.4116   $183.41   $183.40   $183.40  
  Purchase #7 $212.29   8.692%   $230.7422   $230.74   $230.75   $230.70  
  7 purchase totals = $936.13       $1,023.2177   $1,023.21   $1,023.20   $1,023.10