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 $149.67   8.355%   $162.1749   $162.17   $162.15   $162.20  
  Purchase #2 $72.27   7.577%   $77.7459   $77.75   $77.75   $77.70  
  Purchase #3 $11.97   6.710%   $12.7732   $12.77   $12.75   $12.80  
  Purchase #4 $39.54   11.283%   $44.0013   $44.00   $44.00   $44.00  
  Purchase #5 $191.86   12.600%   $216.0344   $216.03   $216.05   $216.00  
  Purchase #6 $90.49   5.161%   $95.1602   $95.16   $95.15   $95.20  
  Purchase #7 $162.61   12.453%   $182.8598   $182.86   $182.85   $182.90  
  7 purchase totals = $718.41       $790.7497   $790.74   $790.70   $790.80