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 $239.72   5.774%   $253.5614   $253.56   $253.55   $253.60  
  Purchase #2 $86.80   4.578%   $90.7737   $90.77   $90.75   $90.80  
  Purchase #3 $137.54   4.844%   $144.2024   $144.20   $144.20   $144.20  
  Purchase #4 $117.64   8.152%   $127.23   $127.23   $127.25   $127.20  
  Purchase #5 $177.28   8.421%   $192.2087   $192.21   $192.20   $192.20  
  Purchase #6 $67.72   13.386%   $76.785   $76.79   $76.80   $76.80  
  Purchase #7 $160.94   5.640%   $170.017   $170.02   $170.00   $170.00  
  7 purchase totals = $987.64       $1,054.7782   $1,054.78   $1,054.75   $1,054.80