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 $178.96   7.136%   $191.7306   $191.73   $191.75   $191.70  
  Purchase #2 $128.93   11.636%   $143.9323   $143.93   $143.95   $143.90  
  Purchase #3 $118.95   12.649%   $133.996   $134.00   $134.00   $134.00  
  Purchase #4 $218.64   10.121%   $240.7686   $240.77   $240.75   $240.80  
  Purchase #5 $109.34   13.822%   $124.453   $124.45   $124.45   $124.50  
  Purchase #6 $248.66   7.802%   $268.0605   $268.06   $268.05   $268.10  
  Purchase #7 $239.81   9.612%   $262.8605   $262.86   $262.85   $262.90  
  7 purchase totals = $1,243.29       $1,365.8015   $1,365.80   $1,365.80   $1,365.90