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 $230.41   10.224%   $253.9671   $253.97   $253.95   $254.00  
  Purchase #2 $193.93   10.454%   $214.2034   $214.20   $214.20   $214.20  
  Purchase #3 $175.30   4.433%   $183.071   $183.07   $183.05   $183.10  
  Purchase #4 $43.52   11.179%   $48.3851   $48.39   $48.40   $48.40  
  Purchase #5 $144.42   8.533%   $156.7434   $156.74   $156.75   $156.70  
  Purchase #6 $47.25   7.793%   $50.9322   $50.93   $50.95   $50.90  
  Purchase #7 $131.85   4.387%   $137.6343   $137.63   $137.65   $137.60  
  7 purchase totals = $966.68       $1,044.9365   $1,044.93   $1,044.95   $1,044.90