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 $35.49   6.380%   $37.7543   $37.75   $37.75   $37.80  
  Purchase #2 $88.71   8.220%   $96.002   $96.00   $96.00   $96.00  
  Purchase #3 $86.66   9.340%   $94.754   $94.75   $94.75   $94.80  
  Purchase #4 $94.97   4.657%   $99.3928   $99.39   $99.40   $99.40  
  Purchase #5 $245.25   5.867%   $259.6388   $259.64   $259.65   $259.60  
  Purchase #6 $181.92   13.136%   $205.817   $205.82   $205.80   $205.80  
  Purchase #7 $187.42   6.283%   $199.1956   $199.20   $199.20   $199.20  
  7 purchase totals = $920.42       $992.5545   $992.55   $992.55   $992.60