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	$155.42	10.295%	$171.4205	$171.42	$171.40	$171.40
Purchase #2	$166.33	13.731%	$189.1688	$189.17	$189.15	$189.20
Purchase #3	$14.58	3.325%	$15.0648	$15.06	$15.05	$15.10
Purchase #4	$89.34	12.740%	$100.7219	$100.72	$100.70	$100.70
Purchase #5	$21.55	13.201%	$24.3948	$24.39	$24.40	$24.40
Purchase #6	$39.74	6.382%	$42.2762	$42.28	$42.30	$42.30
Purchase #7	$43.48	5.177%	$45.731	$45.73	$45.75	$45.70
7 purchase totals =	$530.44		$588.7780	$588.77	$588.75	$588.80