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	$238.56	8.309%	$258.382	$258.38	$258.40	$258.40
Purchase #2	$156.74	4.843%	$164.3309	$164.33	$164.35	$164.30
Purchase #3	$56.46	8.245%	$61.1151	$61.12	$61.10	$61.10
Purchase #4	$159.77	3.361%	$165.1399	$165.14	$165.15	$165.10
Purchase #5	$91.85	9.175%	$100.2772	$100.28	$100.30	$100.30
Purchase #6	$214.97	13.437%	$243.8555	$243.86	$243.85	$243.90
Purchase #7	$131.70	13.477%	$149.4492	$149.45	$149.45	$149.40
7 purchase totals =	$1,050.05		$1,142.5498	$1,142.56	$1,142.60	$1,142.50