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	$48.83	13.821%	$55.5788	$55.58	$55.60	$55.60
Purchase #2	$68.79	12.721%	$77.5408	$77.54	$77.55	$77.50
Purchase #3	$11.69	3.570%	$12.1073	$12.11	$12.10	$12.10
Purchase #4	$100.28	11.449%	$111.7611	$111.76	$111.75	$111.80
Purchase #5	$218.95	6.314%	$232.7745	$232.77	$232.75	$232.80
Purchase #6	$123.60	11.378%	$137.6632	$137.66	$137.65	$137.70
Purchase #7	$35.35	6.736%	$37.7312	$37.73	$37.75	$37.70
7 purchase totals =	$607.49		$665.1569	$665.15	$665.15	$665.20