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 $154.48   13.124%   $174.754   $174.75   $174.75   $174.80  
  Purchase #2 $84.63   8.175%   $91.5485   $91.55   $91.55   $91.50  
  Purchase #3 $152.78   6.528%   $162.7535   $162.75   $162.75   $162.80  
  Purchase #4 $92.39   10.210%   $101.823   $101.82   $101.80   $101.80  
  Purchase #5 $184.87   12.568%   $208.1045   $208.10   $208.10   $208.10  
  Purchase #6 $54.99   10.398%   $60.7079   $60.71   $60.70   $60.70  
  Purchase #7 $179.32   3.807%   $186.1467   $186.15   $186.15   $186.10  
  7 purchase totals = $903.46       $985.8381   $985.83   $985.80   $985.80