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 $94.87   6.186%   $100.7387   $100.74   $100.75   $100.70  
  Purchase #2 $179.68   11.833%   $200.9415   $200.94   $200.95   $200.90  
  Purchase #3 $118.61   7.527%   $127.5378   $127.54   $127.55   $127.50  
  Purchase #4 $163.55   7.816%   $176.3331   $176.33   $176.35   $176.30  
  Purchase #5 $220.79   10.567%   $244.1209   $244.12   $244.10   $244.10  
  Purchase #6 $139.36   13.346%   $157.959   $157.96   $157.95   $158.00  
  Purchase #7 $25.86   3.385%   $26.7354   $26.74   $26.75   $26.70  
  7 purchase totals = $942.72       $1,034.3664   $1,034.37   $1,034.40   $1,034.20