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 $28.97   12.207%   $32.5064   $32.51   $32.50   $32.50  
  Purchase #2 $69.70   4.308%   $72.7027   $72.70   $72.70   $72.70  
  Purchase #3 $36.42   10.401%   $40.208   $40.21   $40.20   $40.20  
  Purchase #4 $176.36   3.685%   $182.8589   $182.86   $182.85   $182.90  
  Purchase #5 $178.48   6.135%   $189.4297   $189.43   $189.45   $189.40  
  Purchase #6 $224.93   9.602%   $246.5278   $246.53   $246.55   $246.50  
  Purchase #7 $222.71   10.578%   $246.2683   $246.27   $246.25   $246.30  
  7 purchase totals = $937.57       $1,010.5018   $1,010.51   $1,010.50   $1,010.50