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	$227.59	11.566%	$253.9131	$253.91	$253.90	$253.90
Purchase #2	$136.46	4.109%	$142.0671	$142.07	$142.05	$142.10
Purchase #3	$165.74	12.288%	$186.1061	$186.11	$186.10	$186.10
Purchase #4	$147.94	7.193%	$158.5813	$158.58	$158.60	$158.60
Purchase #5	$35.60	12.252%	$39.9617	$39.96	$39.95	$40.00
Purchase #6	$39.42	5.769%	$41.6941	$41.69	$41.70	$41.70
Purchase #7	$137.47	6.814%	$146.8372	$146.84	$146.85	$146.80
7 purchase totals =	$890.22		$969.1606	$969.16	$969.15	$969.20