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 $168.48   9.644%   $184.7282   $184.73   $184.75   $184.70  
  Purchase #2 $120.67   12.394%   $135.6258   $135.63   $135.65   $135.60  
  Purchase #3 $119.49   12.648%   $134.6031   $134.60   $134.60   $134.60  
  Purchase #4 $154.89   3.705%   $160.6287   $160.63   $160.65   $160.60  
  Purchase #5 $68.44   4.630%   $71.6088   $71.61   $71.60   $71.60  
  Purchase #6 $84.62   8.116%   $91.4878   $91.49   $91.50   $91.50  
  Purchase #7 $102.66   7.708%   $110.573   $110.57   $110.55   $110.60  
  7 purchase totals = $819.25       $889.2554   $889.26   $889.30   $889.20