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	$20.63	4.378%	$21.5332	$21.53	$21.55	$21.50
Purchase #2	$100.29	10.502%	$110.8225	$110.82	$110.80	$110.80
Purchase #3	$82.89	9.653%	$90.8914	$90.89	$90.90	$90.90
Purchase #4	$191.49	3.747%	$198.6651	$198.67	$198.65	$198.70
Purchase #5	$188.87	8.206%	$204.3687	$204.37	$204.35	$204.40
Purchase #6	$38.38	6.247%	$40.7776	$40.78	$40.80	$40.80
Purchase #7	$187.75	11.327%	$209.0164	$209.02	$209.00	$209.00
7 purchase totals =	$810.30		$876.0749	$876.08	$876.05	$876.10