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	$37.51	9.104%	$40.9249	$40.92	$40.90	$40.90
Purchase #2	$176.81	13.618%	$200.888	$200.89	$200.90	$200.90
Purchase #3	$92.86	7.510%	$99.8338	$99.83	$99.85	$99.80
Purchase #4	$174.63	7.831%	$188.3053	$188.31	$188.30	$188.30
Purchase #5	$60.76	13.201%	$68.7809	$68.78	$68.80	$68.80
Purchase #6	$151.93	11.668%	$169.6572	$169.66	$169.65	$169.70
Purchase #7	$231.89	5.638%	$244.964	$244.96	$244.95	$245.00
7 purchase totals =	$926.39		$1,013.3541	$1,013.35	$1,013.35	$1,013.40