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	$236.55	7.651%	$254.6484	$254.65	$254.65	$254.60
Purchase #2	$58.43	3.401%	$60.4172	$60.42	$60.40	$60.40
Purchase #3	$124.95	10.415%	$137.9635	$137.96	$137.95	$138.00
Purchase #4	$52.68	12.650%	$59.344	$59.34	$59.35	$59.30
Purchase #5	$57.59	3.818%	$59.7888	$59.79	$59.80	$59.80
Purchase #6	$167.67	3.116%	$172.8946	$172.89	$172.90	$172.90
Purchase #7	$240.61	5.764%	$254.4788	$254.48	$254.50	$254.50
7 purchase totals =	$938.48		$999.5353	$999.53	$999.55	$999.50