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 $97.85   12.456%   $110.0382   $110.04   $110.05   $110.00  
  Purchase #2 $10.99   13.241%   $12.4452   $12.45   $12.45   $12.40  
  Purchase #3 $159.83   6.681%   $170.5082   $170.51   $170.50   $170.50  
  Purchase #4 $151.70   5.820%   $160.5289   $160.53   $160.55   $160.50  
  Purchase #5 $60.81   9.383%   $66.5158   $66.52   $66.50   $66.50  
  Purchase #6 $116.76   8.237%   $126.3775   $126.38   $126.40   $126.40  
  Purchase #7 $106.99   7.468%   $114.98   $114.98   $115.00   $115.00  
  7 purchase totals = $704.93       $761.3938   $761.41   $761.45   $761.30