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 $73.92   11.771%   $82.6211   $82.62   $82.60   $82.60  
  Purchase #2 $246.26   9.312%   $269.1917   $269.19   $269.20   $269.20  
  Purchase #3 $177.98   8.126%   $192.4427   $192.44   $192.45   $192.40  
  Purchase #4 $107.79   5.608%   $113.8349   $113.83   $113.85   $113.80  
  Purchase #5 $126.68   7.567%   $136.2659   $136.27   $136.25   $136.30  
  Purchase #6 $54.94   9.828%   $60.3395   $60.34   $60.35   $60.30  
  Purchase #7 $46.75   6.456%   $49.7682   $49.77   $49.75   $49.80  
  7 purchase totals = $834.32       $904.4640   $904.46   $904.45   $904.40