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	$244.88	10.609%	$270.8593	$270.86	$270.85	$270.90
Purchase #2	$141.42	11.770%	$158.0651	$158.07	$158.05	$158.10
Purchase #3	$91.53	10.698%	$101.3219	$101.32	$101.30	$101.30
Purchase #4	$123.65	3.564%	$128.0569	$128.06	$128.05	$128.10
Purchase #5	$12.61	4.416%	$13.1669	$13.17	$13.15	$13.20
Purchase #6	$141.28	3.231%	$145.8448	$145.84	$145.85	$145.80
Purchase #7	$29.74	9.424%	$32.5427	$32.54	$32.55	$32.50
7 purchase totals =	$785.11		$849.8576	$849.86	$849.80	$849.90