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 $41.91   3.149%   $43.2297   $43.23   $43.25   $43.20  
  Purchase #2 $107.56   3.758%   $111.6021   $111.60   $111.60   $111.60  
  Purchase #3 $67.56   11.632%   $75.4186   $75.42   $75.40   $75.40  
  Purchase #4 $127.87   5.144%   $134.4476   $134.45   $134.45   $134.40  
  Purchase #5 $193.44   10.350%   $213.461   $213.46   $213.45   $213.50  
  Purchase #6 $237.60   4.106%   $247.3559   $247.36   $247.35   $247.40  
  Purchase #7 $119.34   13.428%   $135.365   $135.37   $135.35   $135.40  
  7 purchase totals = $895.28       $960.8799   $960.89   $960.85   $960.90