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 $190.57   13.491%   $216.2798   $216.28   $216.30   $216.30  
  Purchase #2 $239.98   8.205%   $259.6704   $259.67   $259.65   $259.70  
  Purchase #3 $50.93   11.798%   $56.9387   $56.94   $56.95   $56.90  
  Purchase #4 $45.71   7.703%   $49.231   $49.23   $49.25   $49.20  
  Purchase #5 $92.76   9.245%   $101.3357   $101.34   $101.35   $101.30  
  Purchase #6 $80.49   4.183%   $83.8569   $83.86   $83.85   $83.90  
  Purchase #7 $232.50   7.577%   $250.1165   $250.12   $250.10   $250.10  
  7 purchase totals = $932.94       $1,017.4290   $1,017.44   $1,017.45   $1,017.40