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 $89.68   3.352%   $92.6861   $92.69   $92.70   $92.70  
  Purchase #2 $17.61   6.698%   $18.7895   $18.79   $18.80   $18.80  
  Purchase #3 $133.91   4.554%   $140.0083   $140.01   $140.00   $140.00  
  Purchase #4 $29.30   9.252%   $32.0108   $32.01   $32.00   $32.00  
  Purchase #5 $122.60   13.412%   $139.0431   $139.04   $139.05   $139.00  
  Purchase #6 $97.93   8.486%   $106.2403   $106.24   $106.25   $106.20  
  Purchase #7 $241.98   3.367%   $250.1275   $250.13   $250.15   $250.10  
  7 purchase totals = $733.01       $778.9056   $778.91   $778.95   $778.80