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 $229.64   3.197%   $236.9816   $236.98   $237.00   $237.00  
  Purchase #2 $184.49   8.578%   $200.3156   $200.32   $200.30   $200.30  
  Purchase #3 $212.66   12.519%   $239.2829   $239.28   $239.30   $239.30  
  Purchase #4 $176.99   10.302%   $195.2235   $195.22   $195.20   $195.20  
  Purchase #5 $88.73   5.509%   $93.6181   $93.62   $93.60   $93.60  
  Purchase #6 $155.51   11.826%   $173.9006   $173.90   $173.90   $173.90  
  Purchase #7 $10.81   11.106%   $12.0106   $12.01   $12.00   $12.00  
  7 purchase totals = $1,058.83       $1,151.3329   $1,151.33   $1,151.30   $1,151.30