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 $34.64   3.417%   $35.8236   $35.82   $35.80   $35.80  
  Purchase #2 $170.93   9.461%   $187.1017   $187.10   $187.10   $187.10  
  Purchase #3 $219.80   3.625%   $227.7678   $227.77   $227.75   $227.80  
  Purchase #4 $68.39   7.873%   $73.7743   $73.77   $73.75   $73.80  
  Purchase #5 $182.85   11.811%   $204.4464   $204.45   $204.45   $204.40  
  Purchase #6 $158.25   3.480%   $163.7571   $163.76   $163.75   $163.80  
  Purchase #7 $158.61   3.164%   $163.6284   $163.63   $163.65   $163.60  
  7 purchase totals = $993.47       $1,056.2993   $1,056.30   $1,056.25   $1,056.30