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	$73.27	13.613%	$83.2442	$83.24	$83.25	$83.20
Purchase #2	$56.88	6.874%	$60.7899	$60.79	$60.80	$60.80
Purchase #3	$19.44	10.547%	$21.4903	$21.49	$21.50	$21.50
Purchase #4	$71.81	6.608%	$76.5552	$76.56	$76.55	$76.60
Purchase #5	$71.46	13.107%	$80.8263	$80.83	$80.85	$80.80
Purchase #6	$158.63	13.415%	$179.9102	$179.91	$179.90	$179.90
Purchase #7	$44.85	12.145%	$50.297	$50.30	$50.30	$50.30
7 purchase totals =	$496.34		$553.1131	$553.12	$553.15	$553.10