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	$12.65	5.104%	$13.2957	$13.30	$13.30	$13.30
Purchase #2	$43.28	12.268%	$48.5896	$48.59	$48.60	$48.60
Purchase #3	$185.94	4.323%	$193.9782	$193.98	$194.00	$194.00
Purchase #4	$83.60	7.168%	$89.5924	$89.59	$89.60	$89.60
Purchase #5	$28.88	8.481%	$31.3293	$31.33	$31.35	$31.30
Purchase #6	$104.30	6.639%	$111.2245	$111.22	$111.20	$111.20
Purchase #7	$175.40	8.281%	$189.9249	$189.92	$189.90	$189.90
7 purchase totals =	$634.05		$677.9346	$677.93	$677.95	$677.90