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 $91.98   6.728%   $98.1684   $98.17   $98.15   $98.20  
  Purchase #2 $177.49   13.463%   $201.3855   $201.39   $201.40   $201.40  
  Purchase #3 $60.75   3.694%   $62.9941   $62.99   $63.00   $63.00  
  Purchase #4 $143.37   5.610%   $151.4131   $151.41   $151.40   $151.40  
  Purchase #5 $247.50   8.128%   $267.6168   $267.62   $267.60   $267.60  
  Purchase #6 $105.68   11.550%   $117.886   $117.89   $117.90   $117.90  
  Purchase #7 $168.39   10.420%   $185.9362   $185.94   $185.95   $185.90  
  7 purchase totals = $995.16       $1,085.4001   $1,085.41   $1,085.40   $1,085.40