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	$82.26	9.270%	$89.8855	$89.89	$89.90	$89.90
Purchase #2	$17.84	10.107%	$19.6431	$19.64	$19.65	$19.60
Purchase #3	$52.32	4.410%	$54.6273	$54.63	$54.65	$54.60
Purchase #4	$207.48	4.560%	$216.9411	$216.94	$216.95	$216.90
Purchase #5	$92.27	7.770%	$99.4394	$99.44	$99.45	$99.40
Purchase #6	$102.39	12.750%	$115.4447	$115.44	$115.45	$115.40
Purchase #7	$85.62	12.667%	$96.4655	$96.47	$96.45	$96.50
7 purchase totals =	$640.18		$692.4466	$692.45	$692.50	$692.30