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	$123.30	3.793%	$127.9768	$127.98	$128.00	$128.00
Purchase #2	$74.92	4.611%	$78.3746	$78.37	$78.35	$78.40
Purchase #3	$141.66	12.294%	$159.0757	$159.08	$159.10	$159.10
Purchase #4	$50.81	7.701%	$54.7229	$54.72	$54.70	$54.70
Purchase #5	$118.54	13.214%	$134.2039	$134.20	$134.20	$134.20
Purchase #6	$179.43	5.580%	$189.4422	$189.44	$189.45	$189.40
Purchase #7	$148.59	12.467%	$167.1147	$167.11	$167.10	$167.10
7 purchase totals =	$837.25		$910.9108	$910.90	$910.90	$910.90