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	$201.90	6.641%	$215.3082	$215.31	$215.30	$215.30
Purchase #2	$79.77	12.598%	$89.8194	$89.82	$89.80	$89.80
Purchase #3	$248.90	12.246%	$279.3803	$279.38	$279.40	$279.40
Purchase #4	$235.73	13.320%	$267.1292	$267.13	$267.15	$267.10
Purchase #5	$21.32	12.814%	$24.0519	$24.05	$24.05	$24.10
Purchase #6	$115.35	4.243%	$120.2443	$120.24	$120.25	$120.20
Purchase #7	$204.55	10.426%	$225.8764	$225.88	$225.90	$225.90
7 purchase totals =	$1,107.52		$1,221.8097	$1,221.81	$1,221.85	$1,221.80