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 $157.83   4.559%   $165.0255   $165.03   $165.05   $165.00  
  Purchase #2 $70.66   8.526%   $76.6845   $76.68   $76.70   $76.70  
  Purchase #3 $25.25   9.579%   $27.6687   $27.67   $27.65   $27.70  
  Purchase #4 $54.86   11.277%   $61.0466   $61.05   $61.05   $61.00  
  Purchase #5 $193.45   6.266%   $205.5716   $205.57   $205.55   $205.60  
  Purchase #6 $114.39   4.836%   $119.9219   $119.92   $119.90   $119.90  
  Purchase #7 $93.47   5.178%   $98.3099   $98.31   $98.30   $98.30  
  7 purchase totals = $709.91       $754.2287   $754.23   $754.20   $754.20