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	$72.42	9.259%	$79.1254	$79.13	$79.15	$79.10
Purchase #2	$197.38	13.344%	$223.7184	$223.72	$223.70	$223.70
Purchase #3	$68.47	4.512%	$71.5594	$71.56	$71.55	$71.60
Purchase #4	$160.34	13.159%	$181.4391	$181.44	$181.45	$181.40
Purchase #5	$27.85	9.603%	$30.5244	$30.52	$30.50	$30.50
Purchase #6	$222.76	6.184%	$236.5355	$236.54	$236.55	$236.50
Purchase #7	$116.94	5.428%	$123.2875	$123.29	$123.30	$123.30
7 purchase totals =	$866.16		$946.1897	$946.20	$946.20	$946.10