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	$105.99	5.300%	$111.6075	$111.61	$111.60	$111.60
Purchase #2	$238.85	7.373%	$256.4604	$256.46	$256.45	$256.50
Purchase #3	$170.44	8.635%	$185.1575	$185.16	$185.15	$185.20
Purchase #4	$90.86	9.484%	$99.4772	$99.48	$99.50	$99.50
Purchase #5	$72.44	3.788%	$75.184	$75.18	$75.20	$75.20
Purchase #6	$24.97	7.206%	$26.7693	$26.77	$26.75	$26.80
Purchase #7	$69.28	9.535%	$75.8858	$75.89	$75.90	$75.90
7 purchase totals =	$772.83		$830.5417	$830.55	$830.55	$830.70