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 $118.82   13.590%   $134.9676   $134.97   $134.95   $135.00  
  Purchase #2 $38.35   4.789%   $40.1866   $40.19   $40.20   $40.20  
  Purchase #3 $219.37   7.718%   $236.301   $236.30   $236.30   $236.30  
  Purchase #4 $121.39   10.148%   $133.7087   $133.71   $133.70   $133.70  
  Purchase #5 $50.54   13.518%   $57.372   $57.37   $57.35   $57.40  
  Purchase #6 $233.81   8.706%   $254.1655   $254.17   $254.15   $254.20  
  Purchase #7 $86.96   5.381%   $91.6393   $91.64   $91.65   $91.60  
  7 purchase totals = $869.24       $948.3407   $948.35   $948.30   $948.40