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	$81.32	11.141%	$90.3799	$90.38	$90.40	$90.40
Purchase #2	$107.52	3.824%	$111.6316	$111.63	$111.65	$111.60
Purchase #3	$162.96	3.646%	$168.9015	$168.90	$168.90	$168.90
Purchase #4	$118.27	13.729%	$134.5073	$134.51	$134.50	$134.50
Purchase #5	$40.63	13.392%	$46.0712	$46.07	$46.05	$46.10
Purchase #6	$169.93	12.836%	$191.7422	$191.74	$191.75	$191.70
Purchase #7	$229.88	9.396%	$251.4795	$251.48	$251.50	$251.50
7 purchase totals =	$910.51		$994.7132	$994.71	$994.75	$994.70