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 $41.27   12.854%   $46.5748   $46.57   $46.55   $46.60  
  Purchase #2 $125.48   13.686%   $142.6532   $142.65   $142.65   $142.70  
  Purchase #3 $124.83   6.639%   $133.1175   $133.12   $133.10   $133.10  
  Purchase #4 $97.49   9.429%   $106.6823   $106.68   $106.70   $106.70  
  Purchase #5 $15.42   8.491%   $16.7293   $16.73   $16.75   $16.70  
  Purchase #6 $230.54   10.591%   $254.9565   $254.96   $254.95   $255.00  
  Purchase #7 $240.33   3.782%   $249.4193   $249.42   $249.40   $249.40  
  7 purchase totals = $875.36       $950.1329   $950.13   $950.10   $950.20