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	$204.86	6.245%	$217.6535	$217.65	$217.65	$217.70
Purchase #2	$205.43	8.118%	$222.1068	$222.11	$222.10	$222.10
Purchase #3	$179.41	9.456%	$196.375	$196.38	$196.40	$196.40
Purchase #4	$150.38	6.313%	$159.8735	$159.87	$159.85	$159.90
Purchase #5	$221.66	8.288%	$240.0312	$240.03	$240.05	$240.00
Purchase #6	$76.45	5.142%	$80.3811	$80.38	$80.40	$80.40
Purchase #7	$93.91	12.285%	$105.4468	$105.45	$105.45	$105.40
7 purchase totals =	$1,132.10		$1,221.8679	$1,221.87	$1,221.90	$1,221.90