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 $55.74   9.644%   $61.1156   $61.12   $61.10   $61.10  
  Purchase #2 $242.69   9.695%   $266.2188   $266.22   $266.20   $266.20  
  Purchase #3 $149.25   11.744%   $166.7779   $166.78   $166.80   $166.80  
  Purchase #4 $94.81   4.132%   $98.7275   $98.73   $98.75   $98.70  
  Purchase #5 $137.47   7.198%   $147.3651   $147.37   $147.35   $147.40  
  Purchase #6 $58.95   4.186%   $61.4176   $61.42   $61.40   $61.40  
  Purchase #7 $200.68   8.243%   $217.2221   $217.22   $217.20   $217.20  
  7 purchase totals = $939.59       $1,018.8446   $1,018.86   $1,018.80   $1,018.80