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 $230.41   6.770%   $246.0088   $246.01   $246.00   $246.00  
  Purchase #2 $154.33   6.172%   $163.8552   $163.86   $163.85   $163.90  
  Purchase #3 $153.96   9.657%   $168.8279   $168.83   $168.85   $168.80  
  Purchase #4 $152.34   11.868%   $170.4197   $170.42   $170.40   $170.40  
  Purchase #5 $168.84   9.836%   $185.4471   $185.45   $185.45   $185.40  
  Purchase #6 $177.50   7.556%   $190.9119   $190.91   $190.90   $190.90  
  Purchase #7 $214.92   11.826%   $240.3364   $240.34   $240.35   $240.30  
  7 purchase totals = $1,252.30       $1,365.8070   $1,365.82   $1,365.80   $1,365.70