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	$121.37	12.138%	$136.1019	$136.10	$136.10	$136.10
Purchase #2	$39.49	6.571%	$42.0849	$42.08	$42.10	$42.10
Purchase #3	$50.30	8.519%	$54.5851	$54.59	$54.60	$54.60
Purchase #4	$146.37	7.645%	$157.56	$157.56	$157.55	$157.60
Purchase #5	$190.79	3.869%	$198.1717	$198.17	$198.15	$198.20
Purchase #6	$20.78	6.163%	$22.0607	$22.06	$22.05	$22.10
Purchase #7	$33.27	11.403%	$37.0638	$37.06	$37.05	$37.10
7 purchase totals =	$602.37		$647.6281	$647.62	$647.60	$647.80