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	$229.86	13.393%	$260.6451	$260.65	$260.65	$260.60
Purchase #2	$164.89	10.235%	$181.7665	$181.77	$181.75	$181.80
Purchase #3	$50.81	10.854%	$56.3249	$56.32	$56.30	$56.30
Purchase #4	$57.25	4.394%	$59.7656	$59.77	$59.75	$59.80
Purchase #5	$164.72	6.392%	$175.2489	$175.25	$175.25	$175.20
Purchase #6	$123.42	11.315%	$137.385	$137.39	$137.40	$137.40
Purchase #7	$52.56	13.173%	$59.4837	$59.48	$59.50	$59.50
7 purchase totals =	$843.51		$930.6197	$930.63	$930.60	$930.60