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 $50.59   6.634%   $53.9461   $53.95   $53.95   $53.90  
  Purchase #2 $144.63   7.691%   $155.7535   $155.75   $155.75   $155.80  
  Purchase #3 $64.63   4.166%   $67.3225   $67.32   $67.30   $67.30  
  Purchase #4 $114.44   13.792%   $130.2236   $130.22   $130.20   $130.20  
  Purchase #5 $135.61   6.565%   $144.5128   $144.51   $144.50   $144.50  
  Purchase #6 $250.36   8.323%   $271.1975   $271.20   $271.20   $271.20  
  Purchase #7 $184.34   9.224%   $201.3435   $201.34   $201.35   $201.30  
  7 purchase totals = $944.60       $1,024.2995   $1,024.29   $1,024.25   $1,024.20