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 $90.67   5.251%   $95.4311   $95.43   $95.45   $95.40  
  Purchase #2 $186.72   10.833%   $206.9474   $206.95   $206.95   $206.90  
  Purchase #3 $217.89   10.819%   $241.4635   $241.46   $241.45   $241.50  
  Purchase #4 $78.56   7.358%   $84.3404   $84.34   $84.35   $84.30  
  Purchase #5 $25.74   3.613%   $26.67   $26.67   $26.65   $26.70  
  Purchase #6 $241.60   5.776%   $255.5548   $255.55   $255.55   $255.60  
  Purchase #7 $148.62   5.708%   $157.1032   $157.10   $157.10   $157.10  
  7 purchase totals = $989.80       $1,067.5104   $1,067.50   $1,067.50   $1,067.50