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 $56.80   8.846%   $61.8245   $61.82   $61.80   $61.80  
  Purchase #2 $165.29   11.314%   $183.9909   $183.99   $184.00   $184.00  
  Purchase #3 $21.71   7.221%   $23.2777   $23.28   $23.30   $23.30  
  Purchase #4 $12.36   6.681%   $13.1858   $13.19   $13.20   $13.20  
  Purchase #5 $90.78   6.556%   $96.7315   $96.73   $96.75   $96.70  
  Purchase #6 $79.28   6.520%   $84.4491   $84.45   $84.45   $84.40  
  Purchase #7 $198.56   4.862%   $208.214   $208.21   $208.20   $208.20  
  7 purchase totals = $624.78       $671.6735   $671.67   $671.70   $671.60