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 $118.61   6.451%   $126.2615   $126.26   $126.25   $126.30  
  Purchase #2 $71.71   11.360%   $79.8563   $79.86   $79.85   $79.90  
  Purchase #3 $146.99   11.871%   $164.4392   $164.44   $164.45   $164.40  
  Purchase #4 $210.88   3.331%   $217.9044   $217.90   $217.90   $217.90  
  Purchase #5 $34.52   12.369%   $38.7898   $38.79   $38.80   $38.80  
  Purchase #6 $237.65   3.426%   $245.7919   $245.79   $245.80   $245.80  
  Purchase #7 $115.88   12.437%   $130.292   $130.29   $130.30   $130.30  
  7 purchase totals = $936.24       $1,003.3351   $1,003.33   $1,003.35   $1,003.40