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	$79.81	13.866%	$90.8765	$90.88	$90.90	$90.90
Purchase #2	$21.73	8.206%	$23.5132	$23.51	$23.50	$23.50
Purchase #3	$77.29	8.114%	$83.5613	$83.56	$83.55	$83.60
Purchase #4	$165.71	8.277%	$179.4258	$179.43	$179.45	$179.40
Purchase #5	$81.83	9.801%	$89.8502	$89.85	$89.85	$89.90
Purchase #6	$136.34	13.213%	$154.3546	$154.35	$154.35	$154.40
Purchase #7	$109.54	6.512%	$116.6732	$116.67	$116.65	$116.70
7 purchase totals =	$672.25		$738.2548	$738.25	$738.25	$738.40