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	$10.46	12.467%	$11.764	$11.76	$11.75	$11.80
Purchase #2	$104.90	13.352%	$118.9062	$118.91	$118.90	$118.90
Purchase #3	$129.35	11.848%	$144.6754	$144.68	$144.70	$144.70
Purchase #4	$37.25	6.154%	$39.5424	$39.54	$39.55	$39.50
Purchase #5	$190.38	3.244%	$196.5559	$196.56	$196.55	$196.60
Purchase #6	$105.81	7.738%	$113.9976	$114.00	$114.00	$114.00
Purchase #7	$79.95	12.489%	$89.935	$89.94	$89.95	$89.90
7 purchase totals =	$658.10		$715.3765	$715.39	$715.40	$715.40