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	$108.51	6.444%	$115.5024	$115.50	$115.50	$115.50
Purchase #2	$166.84	10.734%	$184.7486	$184.75	$184.75	$184.70
Purchase #3	$97.33	4.321%	$101.5356	$101.54	$101.55	$101.50
Purchase #4	$10.59	11.215%	$11.7777	$11.78	$11.80	$11.80
Purchase #5	$59.61	9.616%	$65.3421	$65.34	$65.35	$65.30
Purchase #6	$10.39	4.343%	$10.8412	$10.84	$10.85	$10.80
Purchase #7	$182.33	7.758%	$196.4752	$196.48	$196.50	$196.50
7 purchase totals =	$635.60		$686.2228	$686.23	$686.30	$686.10