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 $224.37   12.559%   $252.5486   $252.55   $252.55   $252.50  
  Purchase #2 $44.78   11.535%   $49.9454   $49.95   $49.95   $49.90  
  Purchase #3 $108.94   7.462%   $117.0691   $117.07   $117.05   $117.10  
  Purchase #4 $149.32   12.157%   $167.4728   $167.47   $167.45   $167.50  
  Purchase #5 $165.95   7.624%   $178.602   $178.60   $178.60   $178.60  
  Purchase #6 $127.98   11.490%   $142.6849   $142.68   $142.70   $142.70  
  Purchase #7 $148.87   9.659%   $163.2494   $163.25   $163.25   $163.20  
  7 purchase totals = $970.21       $1,071.5722   $1,071.57   $1,071.55   $1,071.50