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	$45.29	12.383%	$50.8983	$50.90	$50.90	$50.90
Purchase #2	$74.29	5.647%	$78.4852	$78.49	$78.50	$78.50
Purchase #3	$207.88	3.481%	$215.1163	$215.12	$215.10	$215.10
Purchase #4	$101.56	4.857%	$106.4928	$106.49	$106.50	$106.50
Purchase #5	$193.28	12.593%	$217.6198	$217.62	$217.60	$217.60
Purchase #6	$249.61	9.336%	$272.9136	$272.91	$272.90	$272.90
Purchase #7	$131.51	12.375%	$147.7844	$147.78	$147.80	$147.80
7 purchase totals =	$1,003.42		$1,089.3104	$1,089.31	$1,089.30	$1,089.30