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 $86.36   11.771%   $96.5254   $96.53   $96.55   $96.50  
  Purchase #2 $237.61   12.863%   $268.1738   $268.17   $268.15   $268.20  
  Purchase #3 $201.66   5.817%   $213.3906   $213.39   $213.40   $213.40  
  Purchase #4 $10.46   7.117%   $11.2044   $11.20   $11.20   $11.20  
  Purchase #5 $74.62   7.420%   $80.1568   $80.16   $80.15   $80.20  
  Purchase #6 $75.82   3.317%   $78.3349   $78.33   $78.35   $78.30  
  Purchase #7 $167.36   5.111%   $175.9138   $175.91   $175.90   $175.90  
  7 purchase totals = $853.89       $923.6997   $923.69   $923.70   $923.70