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 $38.66   12.464%   $43.4786   $43.48   $43.50   $43.50  
  Purchase #2 $208.93   5.551%   $220.5277   $220.53   $220.55   $220.50  
  Purchase #3 $150.69   12.570%   $169.6317   $169.63   $169.65   $169.60  
  Purchase #4 $29.57   12.350%   $33.2219   $33.22   $33.20   $33.20  
  Purchase #5 $66.65   10.572%   $73.6962   $73.70   $73.70   $73.70  
  Purchase #6 $242.60   3.852%   $251.945   $251.95   $251.95   $251.90  
  Purchase #7 $156.97   9.136%   $171.3108   $171.31   $171.30   $171.30  
  7 purchase totals = $894.07       $963.8119   $963.82   $963.85   $963.70