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	$67.83	7.281%	$72.7687	$72.77	$72.75	$72.80
Purchase #2	$193.37	3.709%	$200.5421	$200.54	$200.55	$200.50
Purchase #3	$168.51	12.769%	$190.027	$190.03	$190.05	$190.00
Purchase #4	$32.69	7.585%	$35.1695	$35.17	$35.15	$35.20
Purchase #5	$205.28	3.571%	$212.6105	$212.61	$212.60	$212.60
Purchase #6	$15.41	13.746%	$17.5283	$17.53	$17.55	$17.50
Purchase #7	$53.55	9.373%	$58.5692	$58.57	$58.55	$58.60
7 purchase totals =	$736.64		$787.2153	$787.22	$787.20	$787.20