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 $91.36   5.240%   $96.1473   $96.15   $96.15   $96.10  
  Purchase #2 $227.26   6.396%   $241.7955   $241.80   $241.80   $241.80  
  Purchase #3 $69.54   8.214%   $75.252   $75.25   $75.25   $75.30  
  Purchase #4 $132.55   6.599%   $141.297   $141.30   $141.30   $141.30  
  Purchase #5 $191.44   12.146%   $214.6923   $214.69   $214.70   $214.70  
  Purchase #6 $121.80   7.636%   $131.1006   $131.10   $131.10   $131.10  
  Purchase #7 $27.97   4.551%   $29.2429   $29.24   $29.25   $29.20  
  7 purchase totals = $861.92       $929.5276   $929.53   $929.55   $929.50