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	$49.62	11.469%	$55.3109	$55.31	$55.30	$55.30
Purchase #2	$73.86	5.871%	$78.1963	$78.20	$78.20	$78.20
Purchase #3	$188.38	5.333%	$198.4263	$198.43	$198.45	$198.40
Purchase #4	$221.76	13.454%	$251.5956	$251.60	$251.60	$251.60
Purchase #5	$7.45	12.338%	$8.3692	$8.37	$8.35	$8.40
Purchase #6	$17.73	12.303%	$19.9113	$19.91	$19.90	$19.90
Purchase #7	$25.61	11.625%	$28.5872	$28.59	$28.60	$28.60
7 purchase totals =	$584.41		$640.3968	$640.41	$640.40	$640.40