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 $11.73   8.493%   $12.7262   $12.73   $12.75   $12.70  
  Purchase #2 $180.90   10.851%   $200.5295   $200.53   $200.55   $200.50  
  Purchase #3 $68.26   11.111%   $75.8444   $75.84   $75.85   $75.80  
  Purchase #4 $197.90   8.604%   $214.9273   $214.93   $214.95   $214.90  
  Purchase #5 $225.75   9.577%   $247.3701   $247.37   $247.35   $247.40  
  Purchase #6 $115.91   5.233%   $121.9756   $121.98   $122.00   $122.00  
  Purchase #7 $75.89   9.133%   $82.821   $82.82   $82.80   $82.80  
  7 purchase totals = $876.34       $956.1941   $956.20   $956.25   $956.10