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 $79.59   9.266%   $86.9648   $86.96   $86.95   $87.00  
  Purchase #2 $168.75   6.223%   $179.2513   $179.25   $179.25   $179.30  
  Purchase #3 $211.58   11.548%   $236.0133   $236.01   $236.00   $236.00  
  Purchase #4 $25.28   12.169%   $28.3563   $28.36   $28.35   $28.40  
  Purchase #5 $116.90   6.105%   $124.0367   $124.04   $124.05   $124.00  
  Purchase #6 $236.38   3.214%   $243.9773   $243.98   $244.00   $244.00  
  Purchase #7 $148.50   12.471%   $167.0194   $167.02   $167.00   $167.00  
  7 purchase totals = $986.98       $1,065.6191   $1,065.62   $1,065.60   $1,065.70