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 $149.47   9.805%   $164.1255   $164.13   $164.15   $164.10  
  Purchase #2 $24.53   12.261%   $27.5376   $27.54   $27.55   $27.50  
  Purchase #3 $54.40   13.411%   $61.6956   $61.70   $61.70   $61.70  
  Purchase #4 $49.36   3.847%   $51.2589   $51.26   $51.25   $51.30  
  Purchase #5 $79.50   8.186%   $86.0079   $86.01   $86.00   $86.00  
  Purchase #6 $51.47   8.795%   $55.9968   $56.00   $56.00   $56.00  
  Purchase #7 $237.53   13.487%   $269.5657   $269.57   $269.55   $269.60  
  7 purchase totals = $646.26       $716.1880   $716.21   $716.20   $716.20