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	$95.72	9.732%	$105.0355	$105.04	$105.05	$105.00
Purchase #2	$52.61	4.577%	$55.018	$55.02	$55.00	$55.00
Purchase #3	$70.85	10.692%	$78.4253	$78.43	$78.45	$78.40
Purchase #4	$47.74	12.207%	$53.5676	$53.57	$53.55	$53.60
Purchase #5	$131.74	13.430%	$149.4327	$149.43	$149.45	$149.40
Purchase #6	$6.37	13.290%	$7.2166	$7.22	$7.20	$7.20
Purchase #7	$153.82	8.614%	$167.0701	$167.07	$167.05	$167.10
7 purchase totals =	$558.85		$615.7658	$615.78	$615.75	$615.70