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 $49.63   10.107%   $54.6461   $54.65   $54.65   $54.60  
  Purchase #2 $88.98   8.387%   $96.4428   $96.44   $96.45   $96.40  
  Purchase #3 $221.50   12.676%   $249.5773   $249.58   $249.60   $249.60  
  Purchase #4 $241.30   13.651%   $274.2399   $274.24   $274.25   $274.20  
  Purchase #5 $179.74   7.792%   $193.7453   $193.75   $193.75   $193.70  
  Purchase #6 $144.92   4.794%   $151.8675   $151.87   $151.85   $151.90  
  Purchase #7 $64.40   3.174%   $66.4441   $66.44   $66.45   $66.40  
  7 purchase totals = $990.47       $1,086.9630   $1,086.97   $1,087.00   $1,086.80