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 $78.64   5.455%   $82.9298   $82.93   $82.95   $82.90  
  Purchase #2 $66.32   8.364%   $71.867   $71.87   $71.85   $71.90  
  Purchase #3 $19.71   12.794%   $22.2317   $22.23   $22.25   $22.20  
  Purchase #4 $91.27   4.334%   $95.2256   $95.23   $95.25   $95.20  
  Purchase #5 $182.53   5.746%   $193.0182   $193.02   $193.00   $193.00  
  Purchase #6 $85.43   6.851%   $91.2828   $91.28   $91.30   $91.30  
  Purchase #7 $102.92   11.108%   $114.3524   $114.35   $114.35   $114.40  
  7 purchase totals = $626.82       $670.9075   $670.91   $670.95   $670.90