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 $33.97   4.394%   $35.4626   $35.46   $35.45   $35.50  
  Purchase #2 $249.53   13.674%   $283.6507   $283.65   $283.65   $283.70  
  Purchase #3 $22.62   9.596%   $24.7906   $24.79   $24.80   $24.80  
  Purchase #4 $234.29   10.197%   $258.1806   $258.18   $258.20   $258.20  
  Purchase #5 $66.55   5.447%   $70.175   $70.18   $70.20   $70.20  
  Purchase #6 $136.26   11.750%   $152.2706   $152.27   $152.25   $152.30  
  Purchase #7 $194.78   12.404%   $218.9405   $218.94   $218.95   $218.90  
  7 purchase totals = $938.00       $1,043.4706   $1,043.47   $1,043.50   $1,043.60