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	$81.39	6.639%	$86.7935	$86.79	$86.80	$86.80
Purchase #2	$78.58	13.114%	$88.885	$88.89	$88.90	$88.90
Purchase #3	$62.27	6.635%	$66.4016	$66.40	$66.40	$66.40
Purchase #4	$35.78	7.311%	$38.3959	$38.40	$38.40	$38.40
Purchase #5	$236.47	3.498%	$244.7417	$244.74	$244.75	$244.70
Purchase #6	$88.69	11.849%	$99.1989	$99.20	$99.20	$99.20
Purchase #7	$142.52	5.166%	$149.8826	$149.88	$149.90	$149.90
7 purchase totals =	$725.70		$774.2992	$774.30	$774.35	$774.30