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 $58.86   13.829%   $66.9997   $67.00   $67.00   $67.00  
  Purchase #2 $182.78   3.530%   $189.2321   $189.23   $189.25   $189.20  
  Purchase #3 $133.46   8.239%   $144.4558   $144.46   $144.45   $144.50  
  Purchase #4 $231.91   9.441%   $253.8046   $253.80   $253.80   $253.80  
  Purchase #5 $92.93   6.288%   $98.7734   $98.77   $98.75   $98.80  
  Purchase #6 $22.74   3.513%   $23.5389   $23.54   $23.55   $23.50  
  Purchase #7 $144.40   8.135%   $156.1469   $156.15   $156.15   $156.10  
  7 purchase totals = $867.08       $932.9514   $932.95   $932.95   $932.90