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	$55.97	8.281%	$60.6049	$60.60	$60.60	$60.60
Purchase #2	$54.33	3.559%	$56.2636	$56.26	$56.25	$56.30
Purchase #3	$109.78	13.200%	$124.271	$124.27	$124.25	$124.30
Purchase #4	$150.26	6.649%	$160.2508	$160.25	$160.25	$160.30
Purchase #5	$126.48	3.608%	$131.0434	$131.04	$131.05	$131.00
Purchase #6	$97.78	3.766%	$101.4624	$101.46	$101.45	$101.50
Purchase #7	$176.49	13.447%	$200.2226	$200.22	$200.20	$200.20
7 purchase totals =	$771.09		$834.1187	$834.10	$834.05	$834.20