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	$97.26	12.266%	$109.1899	$109.19	$109.20	$109.20
Purchase #2	$250.38	8.193%	$270.8936	$270.89	$270.90	$270.90
Purchase #3	$41.73	11.542%	$46.5465	$46.55	$46.55	$46.50
Purchase #4	$140.48	7.784%	$151.415	$151.42	$151.40	$151.40
Purchase #5	$10.33	4.712%	$10.8167	$10.82	$10.80	$10.80
Purchase #6	$145.65	8.598%	$158.173	$158.17	$158.15	$158.20
Purchase #7	$217.86	6.169%	$231.2998	$231.30	$231.30	$231.30
7 purchase totals =	$903.69		$978.3345	$978.34	$978.30	$978.30