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	$61.29	3.465%	$63.4137	$63.41	$63.40	$63.40
Purchase #2	$53.69	11.519%	$59.8746	$59.87	$59.85	$59.90
Purchase #3	$243.71	11.390%	$271.4686	$271.47	$271.45	$271.50
Purchase #4	$165.65	9.445%	$181.2956	$181.30	$181.30	$181.30
Purchase #5	$184.47	13.637%	$209.6262	$209.63	$209.65	$209.60
Purchase #6	$211.60	9.366%	$231.4185	$231.42	$231.40	$231.40
Purchase #7	$119.36	12.725%	$134.5486	$134.55	$134.55	$134.50
7 purchase totals =	$1,039.77		$1,151.6458	$1,151.65	$1,151.60	$1,151.60