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 $65.56   11.431%   $73.0542   $73.05   $73.05   $73.10  
  Purchase #2 $22.96   3.109%   $23.6738   $23.67   $23.65   $23.70  
  Purchase #3 $242.97   12.773%   $274.0046   $274.00   $274.00   $274.00  
  Purchase #4 $249.80   7.202%   $267.7906   $267.79   $267.80   $267.80  
  Purchase #5 $215.53   3.186%   $222.3968   $222.40   $222.40   $222.40  
  Purchase #6 $115.43   8.684%   $125.4539   $125.45   $125.45   $125.50  
  Purchase #7 $29.93   3.483%   $30.9725   $30.97   $30.95   $31.00  
  7 purchase totals = $942.18       $1,017.3464   $1,017.33   $1,017.30   $1,017.50