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 $91.95   13.482%   $104.3467   $104.35   $104.35   $104.30  
  Purchase #2 $53.35   8.270%   $57.762   $57.76   $57.75   $57.80  
  Purchase #3 $148.46   13.538%   $168.5585   $168.56   $168.55   $168.60  
  Purchase #4 $215.40   8.268%   $233.2093   $233.21   $233.20   $233.20  
  Purchase #5 $114.36   9.567%   $125.3008   $125.30   $125.30   $125.30  
  Purchase #6 $106.89   7.829%   $115.2584   $115.26   $115.25   $115.30  
  Purchase #7 $141.96   10.191%   $156.4271   $156.43   $156.45   $156.40  
  7 purchase totals = $872.37       $960.8628   $960.87   $960.85   $960.90