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 $164.34   10.460%   $181.53   $181.53   $181.55   $181.50  
  Purchase #2 $80.59   5.749%   $85.2231   $85.22   $85.20   $85.20  
  Purchase #3 $133.82   5.182%   $140.7546   $140.75   $140.75   $140.80  
  Purchase #4 $227.39   12.169%   $255.0611   $255.06   $255.05   $255.10  
  Purchase #5 $162.71   13.817%   $185.1916   $185.19   $185.20   $185.20  
  Purchase #6 $120.64   10.197%   $132.9417   $132.94   $132.95   $132.90  
  Purchase #7 $76.46   3.693%   $79.2837   $79.28   $79.30   $79.30  
  7 purchase totals = $965.95       $1,059.9858   $1,059.97   $1,060.00   $1,060.00