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 $67.72   7.666%   $72.9114   $72.91   $72.90   $72.90  
  Purchase #2 $106.96   8.634%   $116.1949   $116.19   $116.20   $116.20  
  Purchase #3 $199.55   4.231%   $207.993   $207.99   $208.00   $208.00  
  Purchase #4 $84.27   10.769%   $93.345   $93.35   $93.35   $93.30  
  Purchase #5 $88.86   13.354%   $100.7264   $100.73   $100.75   $100.70  
  Purchase #6 $165.49   8.473%   $179.512   $179.51   $179.50   $179.50  
  Purchase #7 $51.42   9.466%   $56.2874   $56.29   $56.30   $56.30  
  7 purchase totals = $764.27       $826.9701   $826.97   $827.00   $826.90