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	$36.91	11.223%	$41.0524	$41.05	$41.05	$41.10
Purchase #2	$232.75	11.734%	$260.0609	$260.06	$260.05	$260.10
Purchase #3	$81.90	4.236%	$85.3693	$85.37	$85.35	$85.40
Purchase #4	$93.55	7.392%	$100.4652	$100.47	$100.45	$100.50
Purchase #5	$128.58	12.497%	$144.6486	$144.65	$144.65	$144.60
Purchase #6	$57.73	3.321%	$59.6472	$59.65	$59.65	$59.60
Purchase #7	$143.52	3.805%	$148.9809	$148.98	$149.00	$149.00
7 purchase totals =	$774.94		$840.2245	$840.23	$840.20	$840.30