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	$63.62	9.224%	$69.4883	$69.49	$69.50	$69.50
Purchase #2	$186.53	4.387%	$194.7131	$194.71	$194.70	$194.70
Purchase #3	$83.67	9.150%	$91.3258	$91.33	$91.35	$91.30
Purchase #4	$11.52	12.611%	$12.9728	$12.97	$12.95	$13.00
Purchase #5	$89.86	10.783%	$99.5496	$99.55	$99.55	$99.50
Purchase #6	$49.36	10.435%	$54.5107	$54.51	$54.50	$54.50
Purchase #7	$62.66	7.476%	$67.3445	$67.34	$67.35	$67.30
7 purchase totals =	$547.22		$589.9048	$589.90	$589.90	$589.80