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 $85.54   7.502%   $91.9572   $91.96   $91.95   $92.00  
  Purchase #2 $92.31   10.123%   $101.6545   $101.65   $101.65   $101.70  
  Purchase #3 $98.66   10.786%   $109.3015   $109.30   $109.30   $109.30  
  Purchase #4 $85.83   11.793%   $95.9519   $95.95   $95.95   $96.00  
  Purchase #5 $144.62   12.388%   $162.5355   $162.54   $162.55   $162.50  
  Purchase #6 $124.60   12.212%   $139.8162   $139.82   $139.80   $139.80  
  Purchase #7 $227.41   13.379%   $257.8352   $257.84   $257.85   $257.80  
  7 purchase totals = $858.97       $959.0520   $959.06   $959.05   $959.10