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	$39.69	11.595%	$44.2921	$44.29	$44.30	$44.30
Purchase #2	$247.93	6.822%	$264.8438	$264.84	$264.85	$264.80
Purchase #3	$178.64	7.130%	$191.377	$191.38	$191.40	$191.40
Purchase #4	$35.77	4.563%	$37.4022	$37.40	$37.40	$37.40
Purchase #5	$54.58	3.868%	$56.6912	$56.69	$56.70	$56.70
Purchase #6	$132.61	7.753%	$142.8913	$142.89	$142.90	$142.90
Purchase #7	$60.50	3.865%	$62.8383	$62.84	$62.85	$62.80
7 purchase totals =	$749.72		$800.3359	$800.33	$800.40	$800.30