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	$19.44	3.489%	$20.1183	$20.12	$20.10	$20.10
Purchase #2	$210.28	5.400%	$221.6351	$221.64	$221.65	$221.60
Purchase #3	$120.86	9.286%	$132.0831	$132.08	$132.10	$132.10
Purchase #4	$76.59	7.667%	$82.4622	$82.46	$82.45	$82.50
Purchase #5	$115.44	10.566%	$127.6374	$127.64	$127.65	$127.60
Purchase #6	$94.84	4.500%	$99.1078	$99.11	$99.10	$99.10
Purchase #7	$147.56	12.334%	$165.7601	$165.76	$165.75	$165.80
7 purchase totals =	$785.01		$848.8040	$848.81	$848.80	$848.80