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 $44.61   4.602%   $46.663   $46.66   $46.65   $46.70  
  Purchase #2 $24.25   4.482%   $25.3369   $25.34   $25.35   $25.30  
  Purchase #3 $188.95   13.446%   $214.3562   $214.36   $214.35   $214.40  
  Purchase #4 $41.44   4.651%   $43.3674   $43.37   $43.35   $43.40  
  Purchase #5 $73.43   3.506%   $76.0045   $76.00   $76.00   $76.00  
  Purchase #6 $152.83   9.231%   $166.9377   $166.94   $166.95   $166.90  
  Purchase #7 $175.37   3.343%   $181.2326   $181.23   $181.25   $181.20  
  7 purchase totals = $700.88       $753.8983   $753.90   $753.90   $753.90