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	$16.46	11.769%	$18.3972	$18.40	$18.40	$18.40
Purchase #2	$39.89	4.856%	$41.8271	$41.83	$41.85	$41.80
Purchase #3	$195.39	10.627%	$216.1541	$216.15	$216.15	$216.20
Purchase #4	$116.46	3.478%	$120.5105	$120.51	$120.50	$120.50
Purchase #5	$192.40	10.489%	$212.5808	$212.58	$212.60	$212.60
Purchase #6	$37.30	12.413%	$41.93	$41.93	$41.95	$41.90
Purchase #7	$181.52	10.158%	$199.9588	$199.96	$199.95	$200.00
7 purchase totals =	$779.42		$851.3585	$851.36	$851.40	$851.40