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	$249.45	12.556%	$280.7709	$280.77	$280.75	$280.80
Purchase #2	$89.49	12.761%	$100.9098	$100.91	$100.90	$100.90
Purchase #3	$221.32	4.221%	$230.6619	$230.66	$230.65	$230.70
Purchase #4	$169.78	11.822%	$189.8514	$189.85	$189.85	$189.90
Purchase #5	$139.60	5.526%	$147.3143	$147.31	$147.30	$147.30
Purchase #6	$136.62	5.434%	$144.0439	$144.04	$144.05	$144.00
Purchase #7	$96.76	6.574%	$103.121	$103.12	$103.10	$103.10
7 purchase totals =	$1,103.02		$1,196.6732	$1,196.66	$1,196.60	$1,196.70