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 $210.70   10.676%   $233.1943   $233.19   $233.20   $233.20  
  Purchase #2 $54.73   5.620%   $57.8058   $57.81   $57.80   $57.80  
  Purchase #3 $118.86   4.419%   $124.1124   $124.11   $124.10   $124.10  
  Purchase #4 $27.33   9.462%   $29.916   $29.92   $29.90   $29.90  
  Purchase #5 $9.86   3.353%   $10.1906   $10.19   $10.20   $10.20  
  Purchase #6 $243.77   9.480%   $266.8794   $266.88   $266.90   $266.90  
  Purchase #7 $80.99   4.716%   $84.8095   $84.81   $84.80   $84.80  
  7 purchase totals = $746.24       $806.9080   $806.91   $806.90   $806.90