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 $214.38   8.506%   $232.6152   $232.62   $232.60   $232.60  
  Purchase #2 $22.70   3.802%   $23.5631   $23.56   $23.55   $23.60  
  Purchase #3 $197.59   4.647%   $206.772   $206.77   $206.75   $206.80  
  Purchase #4 $36.43   3.393%   $37.6661   $37.67   $37.65   $37.70  
  Purchase #5 $233.27   5.528%   $246.1652   $246.17   $246.15   $246.20  
  Purchase #6 $55.94   7.777%   $60.2905   $60.29   $60.30   $60.30  
  Purchase #7 $213.68   8.136%   $231.065   $231.07   $231.05   $231.10  
  7 purchase totals = $973.99       $1,038.1371   $1,038.15   $1,038.05   $1,038.30