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	$53.65	5.334%	$56.5117	$56.51	$56.50	$56.50
Purchase #2	$96.32	5.461%	$101.58	$101.58	$101.60	$101.60
Purchase #3	$77.28	11.584%	$86.2321	$86.23	$86.25	$86.20
Purchase #4	$147.65	5.741%	$156.1266	$156.13	$156.15	$156.10
Purchase #5	$96.31	8.580%	$104.5734	$104.57	$104.55	$104.60
Purchase #6	$51.92	3.610%	$53.7943	$53.79	$53.80	$53.80
Purchase #7	$117.76	11.862%	$131.7287	$131.73	$131.75	$131.70
7 purchase totals =	$640.89		$690.5468	$690.54	$690.60	$690.50