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 $55.95   5.354%   $58.9456   $58.95   $58.95   $58.90  
  Purchase #2 $85.53   3.121%   $88.1994   $88.20   $88.20   $88.20  
  Purchase #3 $91.29   5.372%   $96.1941   $96.19   $96.20   $96.20  
  Purchase #4 $188.36   10.576%   $208.281   $208.28   $208.30   $208.30  
  Purchase #5 $78.62   13.233%   $89.0238   $89.02   $89.00   $89.00  
  Purchase #6 $53.55   5.852%   $56.6837   $56.68   $56.70   $56.70  
  Purchase #7 $95.59   3.244%   $98.6909   $98.69   $98.70   $98.70  
  7 purchase totals = $648.89       $696.0185   $696.01   $696.05   $696.00