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 $88.75   8.860%   $96.6133   $96.61   $96.60   $96.60  
  Purchase #2 $121.41   9.271%   $132.6659   $132.67   $132.65   $132.70  
  Purchase #3 $21.71   10.470%   $23.983   $23.98   $24.00   $24.00  
  Purchase #4 $51.59   9.805%   $56.6484   $56.65   $56.65   $56.60  
  Purchase #5 $49.32   6.812%   $52.6797   $52.68   $52.70   $52.70  
  Purchase #6 $226.89   5.345%   $239.0173   $239.02   $239.00   $239.00  
  Purchase #7 $66.73   6.126%   $70.8179   $70.82   $70.80   $70.80  
  7 purchase totals = $626.40       $672.4255   $672.43   $672.40   $672.40