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	$149.29	7.338%	$160.2449	$160.24	$160.25	$160.20
Purchase #2	$61.97	4.265%	$64.613	$64.61	$64.60	$64.60
Purchase #3	$55.81	9.715%	$61.2319	$61.23	$61.25	$61.20
Purchase #4	$120.85	8.812%	$131.4993	$131.50	$131.50	$131.50
Purchase #5	$39.84	6.200%	$42.3101	$42.31	$42.30	$42.30
Purchase #6	$222.90	7.176%	$238.8953	$238.90	$238.90	$238.90
Purchase #7	$69.45	6.282%	$73.8128	$73.81	$73.80	$73.80
7 purchase totals =	$720.11		$772.6073	$772.60	$772.60	$772.50