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 $64.86   6.150%   $68.8489   $68.85   $68.85   $68.80  
  Purchase #2 $62.73   5.817%   $66.379   $66.38   $66.40   $66.40  
  Purchase #3 $98.63   7.169%   $105.7008   $105.70   $105.70   $105.70  
  Purchase #4 $51.77   13.839%   $58.9345   $58.93   $58.95   $58.90  
  Purchase #5 $79.51   8.791%   $86.4997   $86.50   $86.50   $86.50  
  Purchase #6 $150.41   10.326%   $165.9413   $165.94   $165.95   $165.90  
  Purchase #7 $247.82   7.362%   $266.0645   $266.06   $266.05   $266.10  
  7 purchase totals = $755.73       $818.3687   $818.36   $818.40   $818.30