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	$38.94	8.280%	$42.1642	$42.16	$42.15	$42.20
Purchase #2	$32.74	3.690%	$33.9481	$33.95	$33.95	$33.90
Purchase #3	$35.65	13.843%	$40.585	$40.59	$40.60	$40.60
Purchase #4	$101.35	6.259%	$107.6935	$107.69	$107.70	$107.70
Purchase #5	$194.56	10.874%	$215.7165	$215.72	$215.70	$215.70
Purchase #6	$68.53	7.773%	$73.8568	$73.86	$73.85	$73.90
Purchase #7	$55.51	11.827%	$62.0752	$62.08	$62.10	$62.10
7 purchase totals =	$527.28		$576.0393	$576.05	$576.05	$576.10