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	$113.86	12.241%	$127.7976	$127.80	$127.80	$127.80
Purchase #2	$134.73	5.257%	$141.8128	$141.81	$141.80	$141.80
Purchase #3	$67.51	6.310%	$71.7699	$71.77	$71.75	$71.80
Purchase #4	$171.87	9.264%	$187.792	$187.79	$187.80	$187.80
Purchase #5	$134.70	10.181%	$148.4138	$148.41	$148.40	$148.40
Purchase #6	$83.68	9.248%	$91.4187	$91.42	$91.40	$91.40
Purchase #7	$115.44	10.680%	$127.769	$127.77	$127.75	$127.80
7 purchase totals =	$821.79		$896.7738	$896.77	$896.70	$896.80