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 $61.72   11.594%   $68.8758   $68.88   $68.90   $68.90  
  Purchase #2 $222.66   4.637%   $232.9847   $232.98   $233.00   $233.00  
  Purchase #3 $90.34   10.349%   $99.6893   $99.69   $99.70   $99.70  
  Purchase #4 $102.47   11.295%   $114.044   $114.04   $114.05   $114.00  
  Purchase #5 $179.82   7.856%   $193.9467   $193.95   $193.95   $193.90  
  Purchase #6 $126.59   7.348%   $135.8918   $135.89   $135.90   $135.90  
  Purchase #7 $156.60   3.513%   $162.1014   $162.10   $162.10   $162.10  
  7 purchase totals = $940.20       $1,007.5337   $1,007.53   $1,007.60   $1,007.50