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 $249.27   13.379%   $282.6198   $282.62   $282.60   $282.60  
  Purchase #2 $210.92   7.317%   $226.353   $226.35   $226.35   $226.40  
  Purchase #3 $125.93   11.321%   $140.1865   $140.19   $140.20   $140.20  
  Purchase #4 $188.64   12.542%   $212.2992   $212.30   $212.30   $212.30  
  Purchase #5 $65.33   12.487%   $73.4878   $73.49   $73.50   $73.50  
  Purchase #6 $9.84   10.424%   $10.8657   $10.87   $10.85   $10.90  
  Purchase #7 $206.98   5.134%   $217.6064   $217.61   $217.60   $217.60  
  7 purchase totals = $1,056.91       $1,163.4184   $1,163.43   $1,163.40   $1,163.50