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	$92.50	6.429%	$98.4468	$98.45	$98.45	$98.40
Purchase #2	$226.72	5.339%	$238.8246	$238.82	$238.80	$238.80
Purchase #3	$171.61	5.190%	$180.5166	$180.52	$180.50	$180.50
Purchase #4	$57.86	3.144%	$59.6791	$59.68	$59.70	$59.70
Purchase #5	$208.64	3.745%	$216.4536	$216.45	$216.45	$216.50
Purchase #6	$216.83	12.458%	$243.8427	$243.84	$243.85	$243.80
Purchase #7	$231.70	5.294%	$243.9662	$243.97	$243.95	$244.00
7 purchase totals =	$1,205.86		$1,281.7296	$1,281.73	$1,281.70	$1,281.70