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 $99.48   9.498%   $108.9286   $108.93   $108.95   $108.90  
  Purchase #2 $222.33   11.403%   $247.6823   $247.68   $247.70   $247.70  
  Purchase #3 $128.36   13.563%   $145.7695   $145.77   $145.75   $145.80  
  Purchase #4 $22.66   5.411%   $23.8861   $23.89   $23.90   $23.90  
  Purchase #5 $110.62   9.809%   $121.4707   $121.47   $121.45   $121.50  
  Purchase #6 $69.58   4.789%   $72.9122   $72.91   $72.90   $72.90  
  Purchase #7 $175.63   8.117%   $189.8859   $189.89   $189.90   $189.90  
  7 purchase totals = $828.66       $910.5353   $910.54   $910.55   $910.60