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	$234.70	4.185%	$244.5222	$244.52	$244.50	$244.50
Purchase #2	$90.25	6.809%	$96.3951	$96.40	$96.40	$96.40
Purchase #3	$234.77	9.751%	$257.6624	$257.66	$257.65	$257.70
Purchase #4	$11.95	3.184%	$12.3305	$12.33	$12.35	$12.30
Purchase #5	$70.69	10.831%	$78.3464	$78.35	$78.35	$78.30
Purchase #6	$110.76	11.620%	$123.6303	$123.63	$123.65	$123.60
Purchase #7	$104.65	11.482%	$116.6659	$116.67	$116.65	$116.70
7 purchase totals =	$857.77		$929.5528	$929.56	$929.55	$929.50