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	$242.27	8.717%	$263.3887	$263.39	$263.40	$263.40
Purchase #2	$104.68	7.453%	$112.4818	$112.48	$112.50	$112.50
Purchase #3	$61.48	4.870%	$64.4741	$64.47	$64.45	$64.50
Purchase #4	$57.51	9.208%	$62.8055	$62.81	$62.80	$62.80
Purchase #5	$24.83	11.799%	$27.7597	$27.76	$27.75	$27.80
Purchase #6	$202.35	5.234%	$212.941	$212.94	$212.95	$212.90
Purchase #7	$89.39	11.428%	$99.6055	$99.61	$99.60	$99.60
7 purchase totals =	$782.51		$843.4563	$843.46	$843.45	$843.50