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 $73.59   3.706%   $76.3172   $76.32   $76.30   $76.30  
  Purchase #2 $217.70   11.321%   $242.3458   $242.35   $242.35   $242.30  
  Purchase #3 $122.81   10.258%   $135.4078   $135.41   $135.40   $135.40  
  Purchase #4 $21.72   9.629%   $23.8114   $23.81   $23.80   $23.80  
  Purchase #5 $209.26   4.259%   $218.1724   $218.17   $218.15   $218.20  
  Purchase #6 $238.39   11.813%   $266.551   $266.55   $266.55   $266.60  
  Purchase #7 $178.67   11.505%   $199.226   $199.23   $199.25   $199.20  
  7 purchase totals = $1,062.14       $1,161.8316   $1,161.84   $1,161.80   $1,161.80