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	$37.64	7.478%	$40.4547	$40.45	$40.45	$40.50
Purchase #2	$57.59	12.848%	$64.9892	$64.99	$65.00	$65.00
Purchase #3	$54.72	12.471%	$61.5441	$61.54	$61.55	$61.50
Purchase #4	$222.87	8.704%	$242.2686	$242.27	$242.25	$242.30
Purchase #5	$121.45	12.581%	$136.7296	$136.73	$136.75	$136.70
Purchase #6	$227.36	11.419%	$253.3222	$253.32	$253.30	$253.30
Purchase #7	$27.87	9.847%	$30.6144	$30.61	$30.60	$30.60
7 purchase totals =	$749.50		$829.9228	$829.91	$829.90	$829.90