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	$86.61	5.768%	$91.6057	$91.61	$91.60	$91.60
Purchase #2	$73.52	5.264%	$77.3901	$77.39	$77.40	$77.40
Purchase #3	$109.45	12.298%	$122.9102	$122.91	$122.90	$122.90
Purchase #4	$56.76	12.845%	$64.0508	$64.05	$64.05	$64.10
Purchase #5	$185.57	13.333%	$210.312	$210.31	$210.30	$210.30
Purchase #6	$71.69	7.186%	$76.8416	$76.84	$76.85	$76.80
Purchase #7	$36.79	5.409%	$38.78	$38.78	$38.80	$38.80
7 purchase totals =	$620.39		$681.8904	$681.89	$681.90	$681.90