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 $61.59   5.861%   $65.1998   $65.20   $65.20   $65.20  
  Purchase #2 $172.55   9.153%   $188.3435   $188.34   $188.35   $188.30  
  Purchase #3 $130.99   6.563%   $139.5869   $139.59   $139.60   $139.60  
  Purchase #4 $60.47   7.148%   $64.7924   $64.79   $64.80   $64.80  
  Purchase #5 $65.74   7.366%   $70.5824   $70.58   $70.60   $70.60  
  Purchase #6 $144.36   12.750%   $162.7659   $162.77   $162.75   $162.80  
  Purchase #7 $25.35   4.165%   $26.4058   $26.41   $26.40   $26.40  
  7 purchase totals = $661.05       $717.6767   $717.68   $717.70   $717.70