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 $190.63   8.483%   $206.8011   $206.80   $206.80   $206.80  
  Purchase #2 $90.43   12.476%   $101.712   $101.71   $101.70   $101.70  
  Purchase #3 $22.92   7.261%   $24.5842   $24.58   $24.60   $24.60  
  Purchase #4 $127.58   6.438%   $135.7936   $135.79   $135.80   $135.80  
  Purchase #5 $195.87   4.834%   $205.3384   $205.34   $205.35   $205.30  
  Purchase #6 $5.80   6.281%   $6.1643   $6.16   $6.15   $6.20  
  Purchase #7 $95.39   11.147%   $106.0231   $106.02   $106.00   $106.00  
  7 purchase totals = $728.62       $786.4167   $786.40   $786.40   $786.40