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	$64.41	12.272%	$72.3144	$72.31	$72.30	$72.30
Purchase #2	$65.77	8.772%	$71.5393	$71.54	$71.55	$71.50
Purchase #3	$128.54	8.747%	$139.7834	$139.78	$139.80	$139.80
Purchase #4	$50.69	7.601%	$54.5429	$54.54	$54.55	$54.50
Purchase #5	$84.42	3.182%	$87.1062	$87.11	$87.10	$87.10
Purchase #6	$91.84	9.610%	$100.6658	$100.67	$100.65	$100.70
Purchase #7	$120.35	10.777%	$133.3201	$133.32	$133.30	$133.30
7 purchase totals =	$606.02		$659.2721	$659.27	$659.25	$659.20