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 $65.33   12.383%   $73.4198   $73.42   $73.40   $73.40  
  Purchase #2 $187.44   9.120%   $204.5345   $204.53   $204.55   $204.50  
  Purchase #3 $71.63   9.414%   $78.3732   $78.37   $78.35   $78.40  
  Purchase #4 $101.87   5.351%   $107.3211   $107.32   $107.30   $107.30  
  Purchase #5 $81.84   13.621%   $92.9874   $92.99   $93.00   $93.00  
  Purchase #6 $232.61   4.146%   $242.254   $242.25   $242.25   $242.30  
  Purchase #7 $167.88   3.154%   $173.1749   $173.17   $173.15   $173.20  
  7 purchase totals = $908.60       $972.0649   $972.05   $972.00   $972.10