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	$80.78	11.129%	$89.77	$89.77	$89.75	$89.80
Purchase #2	$74.99	11.611%	$83.6971	$83.70	$83.70	$83.70
Purchase #3	$69.51	3.143%	$71.6947	$71.69	$71.70	$71.70
Purchase #4	$90.54	7.796%	$97.5985	$97.60	$97.60	$97.60
Purchase #5	$115.67	5.593%	$122.1394	$122.14	$122.15	$122.10
Purchase #6	$231.82	13.512%	$263.1435	$263.14	$263.15	$263.10
Purchase #7	$156.49	8.539%	$169.8527	$169.85	$169.85	$169.90
7 purchase totals =	$819.80		$897.8959	$897.89	$897.90	$897.90