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	$93.54	12.540%	$105.2699	$105.27	$105.25	$105.30
Purchase #2	$61.92	8.587%	$67.2371	$67.24	$67.25	$67.20
Purchase #3	$83.68	6.602%	$89.2046	$89.20	$89.20	$89.20
Purchase #4	$163.69	12.588%	$184.2953	$184.30	$184.30	$184.30
Purchase #5	$57.34	3.399%	$59.289	$59.29	$59.30	$59.30
Purchase #6	$52.51	11.765%	$58.6878	$58.69	$58.70	$58.70
Purchase #7	$68.95	13.122%	$77.9976	$78.00	$78.00	$78.00
7 purchase totals =	$581.63		$641.9813	$641.99	$642.00	$642.00