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	$70.98	3.396%	$73.3905	$73.39	$73.40	$73.40
Purchase #2	$144.28	8.350%	$156.3274	$156.33	$156.35	$156.30
Purchase #3	$133.35	5.188%	$140.2682	$140.27	$140.25	$140.30
Purchase #4	$228.50	6.808%	$244.0563	$244.06	$244.05	$244.10
Purchase #5	$89.29	13.613%	$101.445	$101.45	$101.45	$101.40
Purchase #6	$126.93	11.790%	$141.895	$141.90	$141.90	$141.90
Purchase #7	$89.76	10.858%	$99.5061	$99.51	$99.50	$99.50
7 purchase totals =	$883.09		$956.8885	$956.91	$956.90	$956.90