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 $23.44   7.106%   $25.1056   $25.11   $25.10   $25.10  
  Purchase #2 $115.43   10.612%   $127.6794   $127.68   $127.70   $127.70  
  Purchase #3 $42.43   10.553%   $46.9076   $46.91   $46.90   $46.90  
  Purchase #4 $221.47   6.640%   $236.1756   $236.18   $236.20   $236.20  
  Purchase #5 $241.82   9.449%   $264.6696   $264.67   $264.65   $264.70  
  Purchase #6 $23.39   11.269%   $26.0258   $26.03   $26.05   $26.00  
  Purchase #7 $36.42   6.531%   $38.7986   $38.80   $38.80   $38.80  
  7 purchase totals = $704.40       $765.3622   $765.38   $765.40   $765.40