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 $30.92   13.578%   $35.1183   $35.12   $35.10   $35.10  
  Purchase #2 $133.59   3.574%   $138.3645   $138.36   $138.35   $138.40  
  Purchase #3 $68.50   7.660%   $73.7471   $73.75   $73.75   $73.70  
  Purchase #4 $75.47   13.394%   $85.5785   $85.58   $85.60   $85.60  
  Purchase #5 $124.94   9.814%   $137.2016   $137.20   $137.20   $137.20  
  Purchase #6 $236.53   5.693%   $249.9957   $250.00   $250.00   $250.00  
  Purchase #7 $211.44   7.747%   $227.8203   $227.82   $227.80   $227.80  
  7 purchase totals = $881.39       $947.8260   $947.83   $947.80   $947.80