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 $235.28   11.298%   $261.8619   $261.86   $261.85   $261.90  
  Purchase #2 $170.66   11.548%   $190.3678   $190.37   $190.35   $190.40  
  Purchase #3 $6.49   12.386%   $7.2939   $7.29   $7.30   $7.30  
  Purchase #4 $205.84   13.583%   $233.7992   $233.80   $233.80   $233.80  
  Purchase #5 $64.79   9.347%   $70.8459   $70.85   $70.85   $70.80  
  Purchase #6 $21.90   3.703%   $22.711   $22.71   $22.70   $22.70  
  Purchase #7 $219.93   9.139%   $240.0294   $240.03   $240.05   $240.00  
  7 purchase totals = $924.89       $1,026.9091   $1,026.91   $1,026.90   $1,026.90