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 $67.63   12.138%   $75.8389   $75.84   $75.85   $75.80  
  Purchase #2 $22.67   3.766%   $23.5238   $23.52   $23.50   $23.50  
  Purchase #3 $98.99   7.824%   $106.735   $106.74   $106.75   $106.70  
  Purchase #4 $30.38   12.382%   $34.1417   $34.14   $34.15   $34.10  
  Purchase #5 $47.38   7.445%   $50.9074   $50.91   $50.90   $50.90  
  Purchase #6 $108.48   11.413%   $120.8608   $120.86   $120.85   $120.90  
  Purchase #7 $48.92   5.535%   $51.6277   $51.63   $51.65   $51.60  
  7 purchase totals = $424.45       $463.6353   $463.64   $463.65   $463.50