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 $95.60   11.641%   $106.7288   $106.73   $106.75   $106.70  
  Purchase #2 $61.83   8.772%   $67.2537   $67.25   $67.25   $67.30  
  Purchase #3 $29.81   3.409%   $30.8262   $30.83   $30.85   $30.80  
  Purchase #4 $226.28   6.382%   $240.7212   $240.72   $240.70   $240.70  
  Purchase #5 $98.99   12.146%   $111.0133   $111.01   $111.00   $111.00  
  Purchase #6 $93.45   4.103%   $97.2843   $97.28   $97.30   $97.30  
  Purchase #7 $60.59   6.395%   $64.4647   $64.46   $64.45   $64.50  
  7 purchase totals = $666.55       $718.2922   $718.28   $718.30   $718.30