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 $239.53   12.513%   $269.5024   $269.50   $269.50   $269.50  
  Purchase #2 $190.28   4.819%   $199.4496   $199.45   $199.45   $199.40  
  Purchase #3 $190.65   5.286%   $200.7278   $200.73   $200.75   $200.70  
  Purchase #4 $160.86   9.855%   $176.7128   $176.71   $176.70   $176.70  
  Purchase #5 $117.26   12.605%   $132.0406   $132.04   $132.05   $132.00  
  Purchase #6 $100.96   11.680%   $112.7521   $112.75   $112.75   $112.80  
  Purchase #7 $54.58   12.563%   $61.4369   $61.44   $61.45   $61.40  
  7 purchase totals = $1,054.12       $1,152.6222   $1,152.62   $1,152.65   $1,152.50