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 $242.70   4.566%   $253.7817   $253.78   $253.80   $253.80  
  Purchase #2 $68.92   9.698%   $75.6039   $75.60   $75.60   $75.60  
  Purchase #3 $202.69   3.807%   $210.4064   $210.41   $210.40   $210.40  
  Purchase #4 $206.28   4.698%   $215.971   $215.97   $215.95   $216.00  
  Purchase #5 $236.43   9.317%   $258.4582   $258.46   $258.45   $258.50  
  Purchase #6 $152.76   7.438%   $164.1223   $164.12   $164.10   $164.10  
  Purchase #7 $24.43   4.743%   $25.5887   $25.59   $25.60   $25.60  
  7 purchase totals = $1,134.21       $1,203.9322   $1,203.93   $1,203.90   $1,204.00