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 $56.67   10.726%   $62.7484   $62.75   $62.75   $62.70  
  Purchase #2 $173.93   3.794%   $180.5289   $180.53   $180.55   $180.50  
  Purchase #3 $230.86   10.673%   $255.4997   $255.50   $255.50   $255.50  
  Purchase #4 $100.77   7.585%   $108.4134   $108.41   $108.40   $108.40  
  Purchase #5 $164.78   11.485%   $183.705   $183.71   $183.70   $183.70  
  Purchase #6 $243.60   3.442%   $251.9847   $251.98   $252.00   $252.00  
  Purchase #7 $27.32   8.567%   $29.6605   $29.66   $29.65   $29.70  
  7 purchase totals = $997.93       $1,072.5406   $1,072.54   $1,072.55   $1,072.50