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	$53.60	6.139%	$56.8905	$56.89	$56.90	$56.90
Purchase #2	$149.82	12.498%	$168.5445	$168.54	$168.55	$168.50
Purchase #3	$55.30	4.505%	$57.7913	$57.79	$57.80	$57.80
Purchase #4	$219.61	6.841%	$234.6335	$234.63	$234.65	$234.60
Purchase #5	$56.79	5.193%	$59.7391	$59.74	$59.75	$59.70
Purchase #6	$99.52	13.472%	$112.9273	$112.93	$112.95	$112.90
Purchase #7	$219.67	4.641%	$229.8649	$229.86	$229.85	$229.90
7 purchase totals =	$854.31		$920.3911	$920.38	$920.45	$920.30