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 $164.26   12.397%   $184.6233   $184.62   $184.60   $184.60  
  Purchase #2 $70.97   3.479%   $73.439   $73.44   $73.45   $73.40  
  Purchase #3 $156.82   11.217%   $174.4105   $174.41   $174.40   $174.40  
  Purchase #4 $103.93   4.340%   $108.4406   $108.44   $108.45   $108.40  
  Purchase #5 $186.57   9.675%   $204.6206   $204.62   $204.60   $204.60  
  Purchase #6 $18.44   11.526%   $20.5654   $20.57   $20.55   $20.60  
  Purchase #7 $28.30   4.206%   $29.4903   $29.49   $29.50   $29.50  
  7 purchase totals = $729.29       $795.5897   $795.59   $795.55   $795.50