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	$113.91	6.766%	$121.6172	$121.62	$121.60	$121.60
Purchase #2	$171.85	5.777%	$181.7778	$181.78	$181.80	$181.80
Purchase #3	$196.47	13.656%	$223.2999	$223.30	$223.30	$223.30
Purchase #4	$105.93	5.558%	$111.8176	$111.82	$111.80	$111.80
Purchase #5	$189.72	4.799%	$198.8247	$198.82	$198.80	$198.80
Purchase #6	$152.78	11.637%	$170.559	$170.56	$170.55	$170.60
Purchase #7	$212.61	7.343%	$228.222	$228.22	$228.20	$228.20
7 purchase totals =	$1,143.27		$1,236.1182	$1,236.12	$1,236.05	$1,236.10