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 $45.27   8.158%   $48.9631   $48.96   $48.95   $49.00  
  Purchase #2 $192.33   13.106%   $217.5368   $217.54   $217.55   $217.50  
  Purchase #3 $195.61   9.276%   $213.7548   $213.75   $213.75   $213.80  
  Purchase #4 $88.41   11.572%   $98.6408   $98.64   $98.65   $98.60  
  Purchase #5 $71.92   8.641%   $78.1346   $78.13   $78.15   $78.10  
  Purchase #6 $9.85   3.589%   $10.2035   $10.20   $10.20   $10.20  
  Purchase #7 $198.88   3.850%   $206.5369   $206.54   $206.55   $206.50  
  7 purchase totals = $802.27       $873.7705   $873.76   $873.80   $873.70