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	$242.68	11.300%	$270.1028	$270.10	$270.10	$270.10
Purchase #2	$93.45	7.194%	$100.1728	$100.17	$100.15	$100.20
Purchase #3	$34.86	12.802%	$39.3228	$39.32	$39.30	$39.30
Purchase #4	$181.31	7.761%	$195.3815	$195.38	$195.40	$195.40
Purchase #5	$19.48	9.751%	$21.3795	$21.38	$21.40	$21.40
Purchase #6	$59.91	8.664%	$65.1006	$65.10	$65.10	$65.10
Purchase #7	$135.74	4.223%	$141.4723	$141.47	$141.45	$141.50
7 purchase totals =	$767.43		$832.9323	$832.92	$832.90	$833.00