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 $100.39   13.559%   $114.0019   $114.00   $114.00   $114.00  
  Purchase #2 $123.78   7.167%   $132.6513   $132.65   $132.65   $132.70  
  Purchase #3 $84.94   12.585%   $95.6297   $95.63   $95.65   $95.60  
  Purchase #4 $88.31   5.123%   $92.8341   $92.83   $92.85   $92.80  
  Purchase #5 $156.65   5.510%   $165.2814   $165.28   $165.30   $165.30  
  Purchase #6 $234.91   12.440%   $264.1328   $264.13   $264.15   $264.10  
  Purchase #7 $60.48   4.823%   $63.397   $63.40   $63.40   $63.40  
  7 purchase totals = $849.46       $927.9282   $927.92   $928.00   $927.90