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   5.146%   $165.9519   $165.95   $165.95   $166.00  
  Purchase #2 $90.34   12.218%   $101.3777   $101.38   $101.40   $101.40  
  Purchase #3 $67.97   5.854%   $71.949   $71.95   $71.95   $71.90  
  Purchase #4 $79.64   11.486%   $88.7875   $88.79   $88.80   $88.80  
  Purchase #5 $148.68   5.140%   $156.3222   $156.32   $156.30   $156.30  
  Purchase #6 $22.89   4.712%   $23.9686   $23.97   $23.95   $24.00  
  Purchase #7 $109.74   6.227%   $116.5735   $116.57   $116.55   $116.60  
  7 purchase totals = $677.09       $724.9304   $724.93   $724.90   $725.00