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 $112.91   6.242%   $119.9578   $119.96   $119.95   $120.00  
  Purchase #2 $182.37   13.211%   $206.4629   $206.46   $206.45   $206.50  
  Purchase #3 $21.60   12.671%   $24.3369   $24.34   $24.35   $24.30  
  Purchase #4 $249.93   6.493%   $266.158   $266.16   $266.15   $266.20  
  Purchase #5 $66.79   12.689%   $75.265   $75.27   $75.25   $75.30  
  Purchase #6 $197.59   3.729%   $204.9581   $204.96   $204.95   $205.00  
  Purchase #7 $122.50   4.549%   $128.0725   $128.07   $128.05   $128.10  
  7 purchase totals = $953.69       $1,025.2112   $1,025.22   $1,025.15   $1,025.40