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	$45.93	13.688%	$52.2169	$52.22	$52.20	$52.20
Purchase #2	$106.36	3.322%	$109.8933	$109.89	$109.90	$109.90
Purchase #3	$76.51	12.630%	$86.1732	$86.17	$86.15	$86.20
Purchase #4	$86.91	5.144%	$91.3807	$91.38	$91.40	$91.40
Purchase #5	$105.70	7.495%	$113.6222	$113.62	$113.60	$113.60
Purchase #6	$72.87	5.573%	$76.931	$76.93	$76.95	$76.90
Purchase #7	$16.27	13.784%	$18.5127	$18.51	$18.50	$18.50
7 purchase totals =	$510.55		$548.7300	$548.72	$548.70	$548.70