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 $76.41   9.482%   $83.6552   $83.66   $83.65   $83.70  
  Purchase #2 $108.77   8.590%   $118.1133   $118.11   $118.10   $118.10  
  Purchase #3 $54.59   5.576%   $57.6339   $57.63   $57.65   $57.60  
  Purchase #4 $127.45   13.125%   $144.1778   $144.18   $144.20   $144.20  
  Purchase #5 $240.71   10.707%   $266.4828   $266.48   $266.50   $266.50  
  Purchase #6 $247.70   8.602%   $269.0072   $269.01   $269.00   $269.00  
  Purchase #7 $113.62   10.867%   $125.9671   $125.97   $125.95   $126.00  
  7 purchase totals = $969.25       $1,065.0373   $1,065.04   $1,065.05   $1,065.10