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	$190.78	10.756%	$211.3003	$211.30	$211.30	$211.30
Purchase #2	$250.32	12.614%	$281.8954	$281.90	$281.90	$281.90
Purchase #3	$35.88	12.359%	$40.3144	$40.31	$40.30	$40.30
Purchase #4	$29.65	4.485%	$30.9798	$30.98	$31.00	$31.00
Purchase #5	$115.47	4.216%	$120.3382	$120.34	$120.35	$120.30
Purchase #6	$85.68	4.847%	$89.8329	$89.83	$89.85	$89.80
Purchase #7	$21.73	7.694%	$23.4019	$23.40	$23.40	$23.40
7 purchase totals =	$729.51		$798.0629	$798.06	$798.10	$798.00