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 $212.71   8.873%   $231.5838   $231.58   $231.60   $231.60  
  Purchase #2 $25.67   3.569%   $26.5862   $26.59   $26.60   $26.60  
  Purchase #3 $163.82   7.543%   $176.1769   $176.18   $176.20   $176.20  
  Purchase #4 $174.58   12.443%   $196.303   $196.30   $196.30   $196.30  
  Purchase #5 $246.55   7.631%   $265.3642   $265.36   $265.35   $265.40  
  Purchase #6 $159.64   4.522%   $166.8589   $166.86   $166.85   $166.90  
  Purchase #7 $178.69   7.686%   $192.4241   $192.42   $192.40   $192.40  
  7 purchase totals = $1,161.66       $1,255.2971   $1,255.29   $1,255.30   $1,255.40