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 $86.62   13.126%   $97.9897   $97.99   $98.00   $98.00  
  Purchase #2 $9.63   4.585%   $10.0715   $10.07   $10.05   $10.10  
  Purchase #3 $95.30   11.541%   $106.2986   $106.30   $106.30   $106.30  
  Purchase #4 $91.92   11.157%   $102.1755   $102.18   $102.20   $102.20  
  Purchase #5 $53.91   8.815%   $58.6622   $58.66   $58.65   $58.70  
  Purchase #6 $209.36   11.771%   $234.0038   $234.00   $234.00   $234.00  
  Purchase #7 $91.53   7.246%   $98.1623   $98.16   $98.15   $98.20  
  7 purchase totals = $638.27       $707.3636   $707.36   $707.35   $707.50