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	$129.55	11.429%	$144.3563	$144.36	$144.35	$144.40
Purchase #2	$46.49	12.145%	$52.1362	$52.14	$52.15	$52.10
Purchase #3	$82.36	4.430%	$86.0085	$86.01	$86.00	$86.00
Purchase #4	$87.86	5.748%	$92.9102	$92.91	$92.90	$92.90
Purchase #5	$202.79	6.387%	$215.7422	$215.74	$215.75	$215.70
Purchase #6	$79.73	12.433%	$89.6428	$89.64	$89.65	$89.60
Purchase #7	$196.72	12.526%	$221.3611	$221.36	$221.35	$221.40
7 purchase totals =	$825.50		$902.1573	$902.16	$902.15	$902.10