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 $196.95   4.762%   $206.3288   $206.33   $206.35   $206.30  
  Purchase #2 $18.66   7.795%   $20.1145   $20.11   $20.10   $20.10  
  Purchase #3 $137.69   7.827%   $148.467   $148.47   $148.45   $148.50  
  Purchase #4 $125.76   13.290%   $142.4735   $142.47   $142.45   $142.50  
  Purchase #5 $178.62   6.572%   $190.3589   $190.36   $190.35   $190.40  
  Purchase #6 $25.66   6.173%   $27.244   $27.24   $27.25   $27.20  
  Purchase #7 $241.43   9.852%   $265.2157   $265.22   $265.20   $265.20  
  7 purchase totals = $924.77       $1,000.2024   $1,000.20   $1,000.15   $1,000.20