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 $58.76   10.666%   $65.0273   $65.03   $65.05   $65.00  
  Purchase #2 $47.87   8.845%   $52.1041   $52.10   $52.10   $52.10  
  Purchase #3 $33.26   6.521%   $35.4289   $35.43   $35.45   $35.40  
  Purchase #4 $67.33   3.664%   $69.797   $69.80   $69.80   $69.80  
  Purchase #5 $91.79   4.347%   $95.7801   $95.78   $95.80   $95.80  
  Purchase #6 $192.63   13.137%   $217.9358   $217.94   $217.95   $217.90  
  Purchase #7 $242.38   10.481%   $267.7838   $267.78   $267.80   $267.80  
  7 purchase totals = $734.02       $803.8570   $803.86   $803.95   $803.80