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	$81.90	9.437%	$89.6289	$89.63	$89.65	$89.60
Purchase #2	$224.52	10.236%	$247.5019	$247.50	$247.50	$247.50
Purchase #3	$152.57	4.635%	$159.6416	$159.64	$159.65	$159.60
Purchase #4	$211.86	4.304%	$220.9785	$220.98	$221.00	$221.00
Purchase #5	$177.89	10.501%	$196.5702	$196.57	$196.55	$196.60
Purchase #6	$160.35	12.756%	$180.8042	$180.80	$180.80	$180.80
Purchase #7	$193.82	12.270%	$217.6017	$217.60	$217.60	$217.60
7 purchase totals =	$1,202.91		$1,312.7270	$1,312.72	$1,312.75	$1,312.70