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	$149.65	7.298%	$160.5715	$160.57	$160.55	$160.60
Purchase #2	$119.84	6.757%	$127.9376	$127.94	$127.95	$127.90
Purchase #3	$238.70	12.758%	$269.1533	$269.15	$269.15	$269.20
Purchase #4	$216.84	10.760%	$240.172	$240.17	$240.15	$240.20
Purchase #5	$240.28	6.226%	$255.2398	$255.24	$255.25	$255.20
Purchase #6	$200.59	4.832%	$210.2825	$210.28	$210.30	$210.30
Purchase #7	$134.63	3.839%	$139.7984	$139.80	$139.80	$139.80
7 purchase totals =	$1,300.53		$1,403.1551	$1,403.15	$1,403.15	$1,403.20