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	$34.80	8.345%	$37.7041	$37.70	$37.70	$37.70
Purchase #2	$159.55	12.247%	$179.0901	$179.09	$179.10	$179.10
Purchase #3	$50.25	9.460%	$55.0037	$55.00	$55.00	$55.00
Purchase #4	$210.94	6.370%	$224.3769	$224.38	$224.40	$224.40
Purchase #5	$236.46	5.309%	$249.0137	$249.01	$249.00	$249.00
Purchase #6	$231.90	10.209%	$255.5747	$255.57	$255.55	$255.60
Purchase #7	$61.42	4.284%	$64.0512	$64.05	$64.05	$64.10
7 purchase totals =	$985.32		$1,064.8144	$1,064.80	$1,064.80	$1,064.90