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 $183.84   9.741%   $201.7479   $201.75   $201.75   $201.70  
  Purchase #2 $77.91   8.393%   $84.449   $84.45   $84.45   $84.40  
  Purchase #3 $156.95   3.498%   $162.4401   $162.44   $162.45   $162.40  
  Purchase #4 $127.32   6.577%   $135.6938   $135.69   $135.70   $135.70  
  Purchase #5 $214.87   13.252%   $243.3446   $243.34   $243.35   $243.30  
  Purchase #6 $60.81   13.335%   $68.919   $68.92   $68.90   $68.90  
  Purchase #7 $26.37   13.118%   $29.8292   $29.83   $29.85   $29.80  
  7 purchase totals = $848.07       $926.4236   $926.42   $926.45   $926.20