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	$201.51	13.815%	$229.3486	$229.35	$229.35	$229.30
Purchase #2	$98.58	8.357%	$106.8183	$106.82	$106.80	$106.80
Purchase #3	$98.31	5.676%	$103.8901	$103.89	$103.90	$103.90
Purchase #4	$164.83	12.814%	$185.9513	$185.95	$185.95	$186.00
Purchase #5	$78.27	3.624%	$81.1065	$81.11	$81.10	$81.10
Purchase #6	$56.81	9.221%	$62.0485	$62.05	$62.05	$62.00
Purchase #7	$119.78	4.243%	$124.8623	$124.86	$124.85	$124.90
7 purchase totals =	$818.09		$894.0256	$894.03	$894.00	$894.00