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 $92.65   9.609%   $101.5527   $101.55   $101.55   $101.60  
  Purchase #2 $120.97   8.757%   $131.5633   $131.56   $131.55   $131.60  
  Purchase #3 $151.73   9.583%   $166.2703   $166.27   $166.25   $166.30  
  Purchase #4 $208.42   7.808%   $224.6934   $224.69   $224.70   $224.70  
  Purchase #5 $66.46   4.781%   $69.6375   $69.64   $69.65   $69.60  
  Purchase #6 $240.35   10.351%   $265.2286   $265.23   $265.25   $265.20  
  Purchase #7 $176.56   13.585%   $200.5457   $200.55   $200.55   $200.50  
  7 purchase totals = $1,057.14       $1,159.4915   $1,159.49   $1,159.50   $1,159.50