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	$7.31	6.203%	$7.7634	$7.76	$7.75	$7.80
Purchase #2	$199.61	12.171%	$223.9045	$223.90	$223.90	$223.90
Purchase #3	$166.30	11.797%	$185.9184	$185.92	$185.90	$185.90
Purchase #4	$190.79	6.414%	$203.0273	$203.03	$203.05	$203.00
Purchase #5	$210.98	13.112%	$238.6437	$238.64	$238.65	$238.60
Purchase #6	$36.26	6.472%	$38.6067	$38.61	$38.60	$38.60
Purchase #7	$30.37	3.722%	$31.5004	$31.50	$31.50	$31.50
7 purchase totals =	$841.62		$929.3644	$929.36	$929.35	$929.30