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 $236.51   9.196%   $258.2595   $258.26   $258.25   $258.30  
  Purchase #2 $179.91   8.739%   $195.6323   $195.63   $195.65   $195.60  
  Purchase #3 $179.75   8.577%   $195.1672   $195.17   $195.15   $195.20  
  Purchase #4 $87.77   9.576%   $96.1749   $96.17   $96.15   $96.20  
  Purchase #5 $112.63   9.574%   $123.4132   $123.41   $123.40   $123.40  
  Purchase #6 $86.61   10.669%   $95.8504   $95.85   $95.85   $95.90  
  Purchase #7 $55.34   12.630%   $62.3294   $62.33   $62.35   $62.30  
  7 purchase totals = $938.52       $1,026.8269   $1,026.82   $1,026.80   $1,026.90