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 $186.55   8.868%   $203.0933   $203.09   $203.10   $203.10  
  Purchase #2 $59.89   7.757%   $64.5357   $64.54   $64.55   $64.50  
  Purchase #3 $153.79   5.801%   $162.7114   $162.71   $162.70   $162.70  
  Purchase #4 $136.92   7.817%   $147.623   $147.62   $147.60   $147.60  
  Purchase #5 $104.43   4.545%   $109.1763   $109.18   $109.20   $109.20  
  Purchase #6 $227.64   3.691%   $236.0422   $236.04   $236.05   $236.00  
  Purchase #7 $82.63   9.205%   $90.2361   $90.24   $90.25   $90.20  
  7 purchase totals = $951.85       $1,013.4180   $1,013.42   $1,013.45   $1,013.30