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 $138.81   13.696%   $157.8214   $157.82   $157.80   $157.80  
  Purchase #2 $53.64   13.133%   $60.6845   $60.68   $60.70   $60.70  
  Purchase #3 $65.46   7.597%   $70.433   $70.43   $70.45   $70.40  
  Purchase #4 $86.39   5.415%   $91.068   $91.07   $91.05   $91.10  
  Purchase #5 $239.94   13.678%   $272.759   $272.76   $272.75   $272.80  
  Purchase #6 $53.40   13.345%   $60.5262   $60.53   $60.55   $60.50  
  Purchase #7 $25.29   7.727%   $27.2442   $27.24   $27.25   $27.20  
  7 purchase totals = $662.93       $740.5363   $740.53   $740.55   $740.50