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 $54.49   8.311%   $59.0187   $59.02   $59.00   $59.00  
  Purchase #2 $174.48   11.832%   $195.1245   $195.12   $195.10   $195.10  
  Purchase #3 $90.73   6.289%   $96.436   $96.44   $96.45   $96.40  
  Purchase #4 $12.55   10.418%   $13.8575   $13.86   $13.85   $13.90  
  Purchase #5 $192.74   7.130%   $206.4824   $206.48   $206.50   $206.50  
  Purchase #6 $47.78   6.856%   $51.0558   $51.06   $51.05   $51.10  
  Purchase #7 $116.81   13.673%   $132.7814   $132.78   $132.80   $132.80  
  7 purchase totals = $689.58       $754.7563   $754.76   $754.75   $754.80