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 $246.86   6.783%   $263.6045   $263.60   $263.60   $263.60  
  Purchase #2 $104.59   5.825%   $110.6824   $110.68   $110.70   $110.70  
  Purchase #3 $89.75   7.638%   $96.6051   $96.61   $96.60   $96.60  
  Purchase #4 $176.33   10.168%   $194.2592   $194.26   $194.25   $194.30  
  Purchase #5 $240.26   4.810%   $251.8165   $251.82   $251.80   $251.80  
  Purchase #6 $120.42   11.465%   $134.2262   $134.23   $134.25   $134.20  
  Purchase #7 $210.58   6.758%   $224.811   $224.81   $224.80   $224.80  
  7 purchase totals = $1,188.79       $1,276.0049   $1,276.01   $1,276.00   $1,276.00