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	$37.96	6.852%	$40.561	$40.56	$40.55	$40.60
Purchase #2	$52.95	6.130%	$56.1958	$56.20	$56.20	$56.20
Purchase #3	$164.67	9.150%	$179.7373	$179.74	$179.75	$179.70
Purchase #4	$243.36	5.419%	$256.5477	$256.55	$256.55	$256.50
Purchase #5	$65.29	8.310%	$70.7156	$70.72	$70.70	$70.70
Purchase #6	$26.79	3.363%	$27.6909	$27.69	$27.70	$27.70
Purchase #7	$38.84	9.560%	$42.5531	$42.55	$42.55	$42.60
7 purchase totals =	$629.86		$674.0014	$674.01	$674.00	$674.00