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 $212.41   7.815%   $229.0098   $229.01   $229.00   $229.00  
  Purchase #2 $233.49   12.602%   $262.9144   $262.91   $262.90   $262.90  
  Purchase #3 $121.58   4.244%   $126.7399   $126.74   $126.75   $126.70  
  Purchase #4 $67.53   8.769%   $73.4517   $73.45   $73.45   $73.50  
  Purchase #5 $160.27   8.429%   $173.7792   $173.78   $173.80   $173.80  
  Purchase #6 $140.78   11.599%   $157.1091   $157.11   $157.10   $157.10  
  Purchase #7 $59.97   6.849%   $64.0773   $64.08   $64.10   $64.10  
  7 purchase totals = $996.03       $1,087.0814   $1,087.08   $1,087.10   $1,087.10