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	$107.69	12.288%	$120.9229	$120.92	$120.90	$120.90
Purchase #2	$94.91	5.601%	$100.2259	$100.23	$100.25	$100.20
Purchase #3	$79.49	3.161%	$82.0027	$82.00	$82.00	$82.00
Purchase #4	$165.88	6.865%	$177.2677	$177.27	$177.25	$177.30
Purchase #5	$89.65	13.501%	$101.7536	$101.75	$101.75	$101.80
Purchase #6	$39.38	8.676%	$42.7966	$42.80	$42.80	$42.80
Purchase #7	$116.56	9.703%	$127.8698	$127.87	$127.85	$127.90
7 purchase totals =	$693.56		$752.8392	$752.84	$752.80	$752.90