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	$55.63	10.533%	$61.4895	$61.49	$61.50	$61.50
Purchase #2	$129.52	11.262%	$144.1065	$144.11	$144.10	$144.10
Purchase #3	$235.78	5.491%	$248.7267	$248.73	$248.75	$248.70
Purchase #4	$122.45	10.704%	$135.557	$135.56	$135.55	$135.60
Purchase #5	$51.57	11.552%	$57.5274	$57.53	$57.55	$57.50
Purchase #6	$98.72	9.718%	$108.3136	$108.31	$108.30	$108.30
Purchase #7	$72.87	13.738%	$82.8809	$82.88	$82.90	$82.90
7 purchase totals =	$766.54		$838.6016	$838.61	$838.65	$838.60