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	$126.78	3.629%	$131.3808	$131.38	$131.40	$131.40
Purchase #2	$135.47	7.352%	$145.4298	$145.43	$145.45	$145.40
Purchase #3	$74.40	3.819%	$77.2413	$77.24	$77.25	$77.20
Purchase #4	$207.36	4.296%	$216.2682	$216.27	$216.25	$216.30
Purchase #5	$171.43	9.739%	$188.1256	$188.13	$188.15	$188.10
Purchase #6	$194.68	13.771%	$221.4894	$221.49	$221.50	$221.50
Purchase #7	$99.64	9.277%	$108.8836	$108.88	$108.90	$108.90
7 purchase totals =	$1,009.76		$1,088.8187	$1,088.82	$1,088.90	$1,088.80