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 $247.84   4.108%   $258.0213   $258.02   $258.00   $258.00  
  Purchase #2 $125.67   6.154%   $133.4037   $133.40   $133.40   $133.40  
  Purchase #3 $147.79   4.436%   $154.346   $154.35   $154.35   $154.30  
  Purchase #4 $229.44   9.500%   $251.2368   $251.24   $251.25   $251.20  
  Purchase #5 $226.74   9.141%   $247.4663   $247.47   $247.45   $247.50  
  Purchase #6 $215.77   9.562%   $236.4019   $236.40   $236.40   $236.40  
  Purchase #7 $241.76   9.373%   $264.4202   $264.42   $264.40   $264.40  
  7 purchase totals = $1,435.01       $1,545.2962   $1,545.30   $1,545.25   $1,545.20