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 $168.53   10.186%   $185.6965   $185.70   $185.70   $185.70  
  Purchase #2 $32.71   10.826%   $36.2512   $36.25   $36.25   $36.30  
  Purchase #3 $123.94   7.648%   $133.4189   $133.42   $133.40   $133.40  
  Purchase #4 $153.95   8.131%   $166.4677   $166.47   $166.45   $166.50  
  Purchase #5 $30.33   4.131%   $31.5829   $31.58   $31.60   $31.60  
  Purchase #6 $202.62   11.770%   $226.4684   $226.47   $226.45   $226.50  
  Purchase #7 $162.84   5.235%   $171.3647   $171.36   $171.35   $171.40  
  7 purchase totals = $874.92       $951.2503   $951.25   $951.20   $951.40