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	$92.74	8.703%	$100.8112	$100.81	$100.80	$100.80
Purchase #2	$20.38	3.738%	$21.1418	$21.14	$21.15	$21.10
Purchase #3	$229.55	12.644%	$258.5743	$258.57	$258.55	$258.60
Purchase #4	$195.87	4.436%	$204.5588	$204.56	$204.55	$204.60
Purchase #5	$249.61	12.468%	$280.7314	$280.73	$280.75	$280.70
Purchase #6	$86.66	11.552%	$96.671	$96.67	$96.65	$96.70
Purchase #7	$159.95	3.466%	$165.4939	$165.49	$165.50	$165.50
7 purchase totals =	$1,034.76		$1,127.9824	$1,127.97	$1,127.95	$1,128.00