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 $5.34   12.736%   $6.0201   $6.02   $6.00   $6.00  
  Purchase #2 $241.90   8.528%   $262.5292   $262.53   $262.55   $262.50  
  Purchase #3 $151.79   5.855%   $160.6773   $160.68   $160.70   $160.70  
  Purchase #4 $208.87   3.366%   $215.9006   $215.90   $215.90   $215.90  
  Purchase #5 $28.58   9.328%   $31.2459   $31.25   $31.25   $31.20  
  Purchase #6 $229.88   13.315%   $260.4885   $260.49   $260.50   $260.50  
  Purchase #7 $79.98   3.543%   $82.8137   $82.81   $82.80   $82.80  
  7 purchase totals = $946.34       $1,019.6753   $1,019.68   $1,019.70   $1,019.60