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 $207.94   9.664%   $228.0353   $228.04   $228.05   $228.00  
  Purchase #2 $68.50   3.852%   $71.1386   $71.14   $71.15   $71.10  
  Purchase #3 $143.50   8.357%   $155.4923   $155.49   $155.50   $155.50  
  Purchase #4 $63.64   8.273%   $68.9049   $68.90   $68.90   $68.90  
  Purchase #5 $117.58   4.697%   $123.1027   $123.10   $123.10   $123.10  
  Purchase #6 $239.25   5.459%   $252.3107   $252.31   $252.30   $252.30  
  Purchase #7 $109.82   12.847%   $123.9286   $123.93   $123.95   $123.90  
  7 purchase totals = $950.23       $1,022.9131   $1,022.91   $1,022.95   $1,022.80