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 $68.71   6.591%   $73.2387   $73.24   $73.25   $73.20  
  Purchase #2 $79.88   8.313%   $86.5204   $86.52   $86.50   $86.50  
  Purchase #3 $129.78   5.666%   $137.1333   $137.13   $137.15   $137.10  
  Purchase #4 $40.69   5.601%   $42.969   $42.97   $42.95   $43.00  
  Purchase #5 $192.54   7.432%   $206.8496   $206.85   $206.85   $206.80  
  Purchase #6 $41.54   6.465%   $44.2256   $44.23   $44.25   $44.20  
  Purchase #7 $201.54   7.502%   $216.6595   $216.66   $216.65   $216.70  
  7 purchase totals = $754.68       $807.5961   $807.60   $807.60   $807.50