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 $64.51   8.820%   $70.1998   $70.20   $70.20   $70.20  
  Purchase #2 $232.59   12.709%   $262.1499   $262.15   $262.15   $262.10  
  Purchase #3 $162.76   7.322%   $174.6773   $174.68   $174.70   $174.70  
  Purchase #4 $196.93   10.260%   $217.135   $217.14   $217.15   $217.10  
  Purchase #5 $106.32   5.672%   $112.3505   $112.35   $112.35   $112.40  
  Purchase #6 $172.58   3.255%   $178.1975   $178.20   $178.20   $178.20  
  Purchase #7 $166.58   5.726%   $176.1184   $176.12   $176.10   $176.10  
  7 purchase totals = $1,102.27       $1,190.8284   $1,190.84   $1,190.85   $1,190.80