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 $67.62   4.403%   $70.5973   $70.60   $70.60   $70.60  
  Purchase #2 $35.64   3.393%   $36.8493   $36.85   $36.85   $36.80  
  Purchase #3 $113.55   4.217%   $118.3384   $118.34   $118.35   $118.30  
  Purchase #4 $61.99   9.780%   $68.0526   $68.05   $68.05   $68.10  
  Purchase #5 $94.98   10.199%   $104.667   $104.67   $104.65   $104.70  
  Purchase #6 $72.70   4.427%   $75.9184   $75.92   $75.90   $75.90  
  Purchase #7 $192.30   8.451%   $208.5513   $208.55   $208.55   $208.60  
  7 purchase totals = $638.78       $682.9743   $682.98   $682.95   $683.00