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	$152.52	13.418%	$172.9851	$172.99	$173.00	$173.00
Purchase #2	$241.27	3.818%	$250.4817	$250.48	$250.50	$250.50
Purchase #3	$187.27	13.237%	$212.0589	$212.06	$212.05	$212.10
Purchase #4	$184.61	3.786%	$191.5993	$191.60	$191.60	$191.60
Purchase #5	$78.97	9.542%	$86.5053	$86.51	$86.50	$86.50
Purchase #6	$196.54	13.554%	$223.179	$223.18	$223.20	$223.20
Purchase #7	$131.80	4.656%	$137.9366	$137.94	$137.95	$137.90
7 purchase totals =	$1,172.98		$1,274.7459	$1,274.76	$1,274.80	$1,274.80