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	$243.96	5.367%	$257.0533	$257.05	$257.05	$257.10
Purchase #2	$162.64	6.309%	$172.901	$172.90	$172.90	$172.90
Purchase #3	$68.36	13.323%	$77.4676	$77.47	$77.45	$77.50
Purchase #4	$82.50	10.223%	$90.934	$90.93	$90.95	$90.90
Purchase #5	$202.75	12.157%	$227.3983	$227.40	$227.40	$227.40
Purchase #6	$51.68	12.442%	$58.11	$58.11	$58.10	$58.10
Purchase #7	$127.51	6.648%	$135.9869	$135.99	$136.00	$136.00
7 purchase totals =	$939.40		$1,019.8511	$1,019.85	$1,019.85	$1,019.90