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	$50.78	8.584%	$55.139	$55.14	$55.15	$55.10
Purchase #2	$228.56	3.497%	$236.5527	$236.55	$236.55	$236.60
Purchase #3	$59.60	13.282%	$67.5161	$67.52	$67.50	$67.50
Purchase #4	$119.63	12.745%	$134.8768	$134.88	$134.90	$134.90
Purchase #5	$97.95	5.176%	$103.0199	$103.02	$103.00	$103.00
Purchase #6	$187.27	12.614%	$210.8922	$210.89	$210.90	$210.90
Purchase #7	$166.59	5.512%	$175.7724	$175.77	$175.75	$175.80
7 purchase totals =	$910.38		$983.7691	$983.77	$983.75	$983.80