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 $126.55   11.664%   $141.3108   $141.31   $141.30   $141.30  
  Purchase #2 $22.55   7.138%   $24.1596   $24.16   $24.15   $24.20  
  Purchase #3 $97.41   11.379%   $108.4943   $108.49   $108.50   $108.50  
  Purchase #4 $225.77   5.770%   $238.7969   $238.80   $238.80   $238.80  
  Purchase #5 $30.33   6.105%   $32.1816   $32.18   $32.20   $32.20  
  Purchase #6 $181.88   7.415%   $195.3664   $195.37   $195.35   $195.40  
  Purchase #7 $10.31   7.759%   $11.11   $11.11   $11.10   $11.10  
  7 purchase totals = $694.80       $751.4196   $751.42   $751.40   $751.50