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	$73.92	6.474%	$78.7056	$78.71	$78.70	$78.70
Purchase #2	$136.44	13.393%	$154.7134	$154.71	$154.70	$154.70
Purchase #3	$196.89	10.181%	$216.9354	$216.94	$216.95	$216.90
Purchase #4	$215.43	3.355%	$222.6577	$222.66	$222.65	$222.70
Purchase #5	$193.56	6.738%	$206.6021	$206.60	$206.60	$206.60
Purchase #6	$55.67	11.627%	$62.1428	$62.14	$62.15	$62.10
Purchase #7	$29.29	11.618%	$32.6929	$32.69	$32.70	$32.70
7 purchase totals =	$901.20		$974.4499	$974.45	$974.45	$974.40