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 $173.29   10.548%   $191.5686   $191.57   $191.55   $191.60  
  Purchase #2 $227.77   9.745%   $249.9662   $249.97   $249.95   $250.00  
  Purchase #3 $5.98   13.188%   $6.7686   $6.77   $6.75   $6.80  
  Purchase #4 $161.92   12.653%   $182.4077   $182.41   $182.40   $182.40  
  Purchase #5 $172.51   13.663%   $196.08   $196.08   $196.10   $196.10  
  Purchase #6 $66.73   5.181%   $70.1873   $70.19   $70.20   $70.20  
  Purchase #7 $42.82   10.285%   $47.224   $47.22   $47.20   $47.20  
  7 purchase totals = $851.02       $944.2024   $944.21   $944.15   $944.30