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	$79.77	12.215%	$89.5139	$89.51	$89.50	$89.50
Purchase #2	$156.88	6.785%	$167.5243	$167.52	$167.50	$167.50
Purchase #3	$230.39	13.232%	$260.8752	$260.88	$260.90	$260.90
Purchase #4	$227.34	13.430%	$257.8718	$257.87	$257.85	$257.90
Purchase #5	$54.71	5.516%	$57.7278	$57.73	$57.75	$57.70
Purchase #6	$161.77	7.764%	$174.3298	$174.33	$174.35	$174.30
Purchase #7	$231.89	10.745%	$256.8066	$256.81	$256.80	$256.80
7 purchase totals =	$1,142.75		$1,264.6494	$1,264.65	$1,264.65	$1,264.60