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 $93.61   8.368%   $101.4433   $101.44   $101.45   $101.40  
  Purchase #2 $120.42   3.699%   $124.8743   $124.87   $124.85   $124.90  
  Purchase #3 $139.55   6.214%   $148.2216   $148.22   $148.20   $148.20  
  Purchase #4 $38.83   7.327%   $41.6751   $41.68   $41.70   $41.70  
  Purchase #5 $86.40   9.755%   $94.8283   $94.83   $94.85   $94.80  
  Purchase #6 $198.96   7.513%   $213.9079   $213.91   $213.90   $213.90  
  Purchase #7 $11.26   3.737%   $11.6808   $11.68   $11.70   $11.70  
  7 purchase totals = $689.03       $736.6313   $736.63   $736.65   $736.60