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	$133.36	9.182%	$145.6051	$145.61	$145.60	$145.60
Purchase #2	$161.99	10.828%	$179.5303	$179.53	$179.55	$179.50
Purchase #3	$88.51	12.194%	$99.3029	$99.30	$99.30	$99.30
Purchase #4	$33.53	12.645%	$37.7699	$37.77	$37.75	$37.80
Purchase #5	$29.64	7.464%	$31.8523	$31.85	$31.85	$31.90
Purchase #6	$124.98	11.815%	$139.7464	$139.75	$139.75	$139.70
Purchase #7	$202.60	9.450%	$221.7457	$221.75	$221.75	$221.70
7 purchase totals =	$774.61		$855.5526	$855.56	$855.55	$855.50