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	$110.87	8.614%	$120.4203	$120.42	$120.40	$120.40
Purchase #2	$131.95	9.127%	$143.9931	$143.99	$144.00	$144.00
Purchase #3	$44.79	13.674%	$50.9146	$50.91	$50.90	$50.90
Purchase #4	$142.75	3.782%	$148.1488	$148.15	$148.15	$148.10
Purchase #5	$217.89	13.684%	$247.7061	$247.71	$247.70	$247.70
Purchase #6	$99.57	11.746%	$111.2655	$111.27	$111.25	$111.30
Purchase #7	$12.93	3.319%	$13.3591	$13.36	$13.35	$13.40
7 purchase totals =	$760.75		$835.8075	$835.81	$835.75	$835.80