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 $65.99   8.163%   $71.3768   $71.38   $71.40   $71.40  
  Purchase #2 $155.87   5.635%   $164.6533   $164.65   $164.65   $164.70  
  Purchase #3 $109.62   8.831%   $119.3005   $119.30   $119.30   $119.30  
  Purchase #4 $69.97   8.692%   $76.0518   $76.05   $76.05   $76.10  
  Purchase #5 $178.73   7.838%   $192.7389   $192.74   $192.75   $192.70  
  Purchase #6 $246.36   3.330%   $254.5638   $254.56   $254.55   $254.60  
  Purchase #7 $249.60   5.354%   $262.9636   $262.96   $262.95   $263.00  
  7 purchase totals = $1,076.14       $1,141.6487   $1,141.64   $1,141.65   $1,141.80