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	$33.85	11.426%	$37.7177	$37.72	$37.70	$37.70
Purchase #2	$144.69	10.701%	$160.1733	$160.17	$160.15	$160.20
Purchase #3	$219.29	4.807%	$229.8313	$229.83	$229.85	$229.80
Purchase #4	$187.87	11.741%	$209.9278	$209.93	$209.95	$209.90
Purchase #5	$164.33	4.591%	$171.8744	$171.87	$171.85	$171.90
Purchase #6	$196.46	12.122%	$220.2749	$220.27	$220.25	$220.30
Purchase #7	$236.63	6.365%	$251.6915	$251.69	$251.70	$251.70
7 purchase totals =	$1,183.12		$1,281.4909	$1,281.48	$1,281.45	$1,281.50