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 $87.48   12.305%   $98.2444   $98.24   $98.25   $98.20  
  Purchase #2 $127.31   11.456%   $141.8946   $141.89   $141.90   $141.90  
  Purchase #3 $205.91   11.799%   $230.2053   $230.21   $230.20   $230.20  
  Purchase #4 $86.41   9.357%   $94.4954   $94.50   $94.50   $94.50  
  Purchase #5 $124.96   13.354%   $141.6472   $141.65   $141.65   $141.60  
  Purchase #6 $165.43   4.655%   $173.1308   $173.13   $173.15   $173.10  
  Purchase #7 $134.53   7.513%   $144.6372   $144.64   $144.65   $144.60  
  7 purchase totals = $932.03       $1,024.2549   $1,024.26   $1,024.30   $1,024.10