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	$234.46	3.265%	$242.1151	$242.12	$242.10	$242.10
Purchase #2	$113.64	5.868%	$120.3084	$120.31	$120.30	$120.30
Purchase #3	$127.77	4.428%	$133.4277	$133.43	$133.45	$133.40
Purchase #4	$150.55	7.814%	$162.314	$162.31	$162.30	$162.30
Purchase #5	$44.51	7.307%	$47.7623	$47.76	$47.75	$47.80
Purchase #6	$235.59	3.598%	$244.0665	$244.07	$244.05	$244.10
Purchase #7	$168.94	7.489%	$181.5919	$181.59	$181.60	$181.60
7 purchase totals =	$1,075.46		$1,131.5859	$1,131.59	$1,131.55	$1,131.60