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	$88.78	5.873%	$93.994	$93.99	$94.00	$94.00
Purchase #2	$131.52	6.381%	$139.9123	$139.91	$139.90	$139.90
Purchase #3	$165.27	8.104%	$178.6635	$178.66	$178.65	$178.70
Purchase #4	$32.38	10.426%	$35.7559	$35.76	$35.75	$35.80
Purchase #5	$180.67	8.560%	$196.1354	$196.14	$196.15	$196.10
Purchase #6	$189.57	4.639%	$198.3642	$198.36	$198.35	$198.40
Purchase #7	$128.72	12.144%	$144.3518	$144.35	$144.35	$144.40
7 purchase totals =	$916.91		$987.1771	$987.17	$987.15	$987.30