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 $87.71   10.235%   $96.6871   $96.69   $96.70   $96.70  
  Purchase #2 $113.34   10.752%   $125.5263   $125.53   $125.55   $125.50  
  Purchase #3 $236.30   5.530%   $249.3674   $249.37   $249.35   $249.40  
  Purchase #4 $106.45   13.351%   $120.6621   $120.66   $120.65   $120.70  
  Purchase #5 $206.47   8.565%   $224.1542   $224.15   $224.15   $224.20  
  Purchase #6 $182.80   13.578%   $207.6206   $207.62   $207.60   $207.60  
  Purchase #7 $61.82   3.349%   $63.8904   $63.89   $63.90   $63.90  
  7 purchase totals = $994.89       $1,087.9081   $1,087.91   $1,087.90   $1,088.00