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	$24.70	11.431%	$27.5235	$27.52	$27.50	$27.50
Purchase #2	$30.61	10.120%	$33.7077	$33.71	$33.70	$33.70
Purchase #3	$21.33	7.189%	$22.8634	$22.86	$22.85	$22.90
Purchase #4	$35.55	4.208%	$37.0459	$37.05	$37.05	$37.00
Purchase #5	$124.44	4.217%	$129.6876	$129.69	$129.70	$129.70
Purchase #6	$171.34	4.390%	$178.8618	$178.86	$178.85	$178.90
Purchase #7	$101.56	9.779%	$111.4916	$111.49	$111.50	$111.50
7 purchase totals =	$509.53		$541.1815	$541.18	$541.15	$541.20