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	$100.82	13.654%	$114.586	$114.59	$114.60	$114.60
Purchase #2	$185.38	7.322%	$198.9535	$198.95	$198.95	$199.00
Purchase #3	$178.79	7.496%	$192.1921	$192.19	$192.20	$192.20
Purchase #4	$78.32	5.278%	$82.4537	$82.45	$82.45	$82.50
Purchase #5	$19.35	10.252%	$21.3338	$21.33	$21.35	$21.30
Purchase #6	$130.50	4.430%	$136.2812	$136.28	$136.30	$136.30
Purchase #7	$165.99	4.251%	$173.0462	$173.05	$173.05	$173.00
7 purchase totals =	$859.15		$918.8465	$918.84	$918.90	$918.90