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 $118.49   4.671%   $124.0247   $124.02   $124.00   $124.00  
  Purchase #2 $147.67   6.580%   $157.3867   $157.39   $157.40   $157.40  
  Purchase #3 $122.88   11.135%   $136.5627   $136.56   $136.55   $136.60  
  Purchase #4 $116.47   13.769%   $132.5068   $132.51   $132.50   $132.50  
  Purchase #5 $228.49   5.586%   $241.2535   $241.25   $241.25   $241.30  
  Purchase #6 $130.74   11.353%   $145.5829   $145.58   $145.60   $145.60  
  Purchase #7 $132.44   9.443%   $144.9463   $144.95   $144.95   $144.90  
  7 purchase totals = $997.18       $1,082.2636   $1,082.26   $1,082.25   $1,082.30