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	$12.57	7.570%	$13.5215	$13.52	$13.50	$13.50
Purchase #2	$58.81	4.526%	$61.4717	$61.47	$61.45	$61.50
Purchase #3	$95.34	4.120%	$99.268	$99.27	$99.25	$99.30
Purchase #4	$64.65	7.751%	$69.661	$69.66	$69.65	$69.70
Purchase #5	$104.47	6.148%	$110.8928	$110.89	$110.90	$110.90
Purchase #6	$124.96	9.745%	$137.1374	$137.14	$137.15	$137.10
Purchase #7	$76.62	3.606%	$79.3829	$79.38	$79.40	$79.40
7 purchase totals =	$537.42		$571.3353	$571.33	$571.30	$571.40