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 $89.29   6.805%   $95.3662   $95.37   $95.35   $95.40  
  Purchase #2 $198.65   8.126%   $214.7923   $214.79   $214.80   $214.80  
  Purchase #3 $9.86   7.386%   $10.5883   $10.59   $10.60   $10.60  
  Purchase #4 $231.56   7.312%   $248.4917   $248.49   $248.50   $248.50  
  Purchase #5 $21.55   13.802%   $24.5243   $24.52   $24.50   $24.50  
  Purchase #6 $127.27   8.786%   $138.4519   $138.45   $138.45   $138.50  
  Purchase #7 $176.49   6.191%   $187.4165   $187.42   $187.40   $187.40  
  7 purchase totals = $854.67       $919.6312   $919.63   $919.60   $919.70