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 $222.54   13.658%   $252.9345   $252.93   $252.95   $252.90  
  Purchase #2 $99.96   7.346%   $107.3031   $107.30   $107.30   $107.30  
  Purchase #3 $63.29   4.203%   $65.9501   $65.95   $65.95   $66.00  
  Purchase #4 $93.32   3.439%   $96.5293   $96.53   $96.55   $96.50  
  Purchase #5 $117.28   13.873%   $133.5503   $133.55   $133.55   $133.60  
  Purchase #6 $218.65   3.332%   $225.9354   $225.94   $225.95   $225.90  
  Purchase #7 $27.93   6.196%   $29.6605   $29.66   $29.65   $29.70  
  7 purchase totals = $842.97       $911.8632   $911.86   $911.90   $911.90