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	$80.45	4.727%	$84.2529	$84.25	$84.25	$84.30
Purchase #2	$94.37	8.622%	$102.5066	$102.51	$102.50	$102.50
Purchase #3	$242.83	10.303%	$267.8488	$267.85	$267.85	$267.80
Purchase #4	$58.27	4.623%	$60.9638	$60.96	$60.95	$61.00
Purchase #5	$171.48	11.482%	$191.1693	$191.17	$191.15	$191.20
Purchase #6	$155.72	10.699%	$172.3805	$172.38	$172.40	$172.40
Purchase #7	$92.71	9.345%	$101.3737	$101.37	$101.35	$101.40
7 purchase totals =	$895.83		$980.4956	$980.49	$980.45	$980.60