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 $36.63   5.308%   $38.5743   $38.57   $38.55   $38.60  
  Purchase #2 $228.41   4.869%   $239.5313   $239.53   $239.55   $239.50  
  Purchase #3 $161.76   8.548%   $175.5872   $175.59   $175.60   $175.60  
  Purchase #4 $126.50   4.304%   $131.9446   $131.94   $131.95   $131.90  
  Purchase #5 $71.80   7.722%   $77.3444   $77.34   $77.35   $77.30  
  Purchase #6 $32.62   11.443%   $36.3527   $36.35   $36.35   $36.40  
  Purchase #7 $82.66   5.639%   $87.3212   $87.32   $87.30   $87.30  
  7 purchase totals = $740.38       $786.6557   $786.64   $786.65   $786.60