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 $62.86   9.157%   $68.6161   $68.62   $68.60   $68.60  
  Purchase #2 $95.42   4.739%   $99.942   $99.94   $99.95   $99.90  
  Purchase #3 $46.32   3.136%   $47.7726   $47.77   $47.75   $47.80  
  Purchase #4 $21.62   5.527%   $22.8149   $22.81   $22.80   $22.80  
  Purchase #5 $240.56   3.352%   $248.6236   $248.62   $248.60   $248.60  
  Purchase #6 $136.43   12.211%   $153.0895   $153.09   $153.10   $153.10  
  Purchase #7 $61.47   10.412%   $67.8703   $67.87   $67.85   $67.90  
  7 purchase totals = $664.68       $708.7290   $708.72   $708.65   $708.70