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 $91.29   4.801%   $95.6728   $95.67   $95.65   $95.70  
  Purchase #2 $176.33   9.381%   $192.8715   $192.87   $192.85   $192.90  
  Purchase #3 $73.67   12.439%   $82.8338   $82.83   $82.85   $82.80  
  Purchase #4 $72.53   12.680%   $81.7268   $81.73   $81.75   $81.70  
  Purchase #5 $101.81   4.521%   $106.4128   $106.41   $106.40   $106.40  
  Purchase #6 $148.65   9.520%   $162.8015   $162.80   $162.80   $162.80  
  Purchase #7 $249.42   8.488%   $270.5908   $270.59   $270.60   $270.60  
  7 purchase totals = $913.70       $992.9100   $992.90   $992.90   $992.90