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	$63.64	12.370%	$71.5123	$71.51	$71.50	$71.50
Purchase #2	$11.39	7.360%	$12.2283	$12.23	$12.25	$12.20
Purchase #3	$128.78	3.510%	$133.3002	$133.30	$133.30	$133.30
Purchase #4	$241.88	7.209%	$259.3171	$259.32	$259.30	$259.30
Purchase #5	$71.78	6.304%	$76.305	$76.31	$76.30	$76.30
Purchase #6	$238.86	9.373%	$261.2483	$261.25	$261.25	$261.20
Purchase #7	$155.59	6.517%	$165.7298	$165.73	$165.75	$165.70
7 purchase totals =	$911.92		$979.6410	$979.65	$979.65	$979.50