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 $82.90   13.721%   $94.2747   $94.27   $94.25   $94.30  
  Purchase #2 $167.32   5.594%   $176.6799   $176.68   $176.70   $176.70  
  Purchase #3 $176.44   6.433%   $187.7904   $187.79   $187.80   $187.80  
  Purchase #4 $87.95   6.589%   $93.745   $93.75   $93.75   $93.70  
  Purchase #5 $187.60   6.733%   $200.2311   $200.23   $200.25   $200.20  
  Purchase #6 $243.77   11.664%   $272.2033   $272.20   $272.20   $272.20  
  Purchase #7 $157.83   4.640%   $165.1533   $165.15   $165.15   $165.20  
  7 purchase totals = $1,103.81       $1,190.0777   $1,190.07   $1,190.10   $1,190.10