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 $238.53   11.198%   $265.2406   $265.24   $265.25   $265.20  
  Purchase #2 $107.69   11.318%   $119.8784   $119.88   $119.90   $119.90  
  Purchase #3 $225.71   5.609%   $238.3701   $238.37   $238.35   $238.40  
  Purchase #4 $174.49   5.596%   $184.2545   $184.25   $184.25   $184.30  
  Purchase #5 $126.95   3.716%   $131.6675   $131.67   $131.65   $131.70  
  Purchase #6 $181.40   6.468%   $193.133   $193.13   $193.15   $193.10  
  Purchase #7 $212.34   6.621%   $226.399   $226.40   $226.40   $226.40  
  7 purchase totals = $1,267.11       $1,358.9431   $1,358.94   $1,358.95   $1,359.00