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	$250.32	11.656%	$279.4973	$279.50	$279.50	$279.50
Purchase #2	$194.38	8.299%	$210.5116	$210.51	$210.50	$210.50
Purchase #3	$176.54	5.218%	$185.7519	$185.75	$185.75	$185.80
Purchase #4	$219.67	12.718%	$247.6076	$247.61	$247.60	$247.60
Purchase #5	$198.42	13.282%	$224.7741	$224.77	$224.75	$224.80
Purchase #6	$33.97	11.365%	$37.8307	$37.83	$37.85	$37.80
Purchase #7	$65.90	8.330%	$71.3895	$71.39	$71.40	$71.40
7 purchase totals =	$1,139.20		$1,257.3627	$1,257.36	$1,257.35	$1,257.40