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	$104.39	4.323%	$108.9028	$108.90	$108.90	$108.90
Purchase #2	$58.40	12.551%	$65.7298	$65.73	$65.75	$65.70
Purchase #3	$151.53	3.568%	$156.9366	$156.94	$156.95	$156.90
Purchase #4	$66.57	8.519%	$72.2411	$72.24	$72.25	$72.20
Purchase #5	$167.72	7.598%	$180.4634	$180.46	$180.45	$180.50
Purchase #6	$135.74	12.526%	$152.7428	$152.74	$152.75	$152.70
Purchase #7	$131.84	5.805%	$139.4933	$139.49	$139.50	$139.50
7 purchase totals =	$816.19		$876.5098	$876.50	$876.55	$876.40