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	$83.43	6.850%	$89.145	$89.15	$89.15	$89.10
Purchase #2	$184.27	3.797%	$191.2667	$191.27	$191.25	$191.30
Purchase #3	$126.57	13.665%	$143.8658	$143.87	$143.85	$143.90
Purchase #4	$116.26	4.779%	$121.8161	$121.82	$121.80	$121.80
Purchase #5	$147.33	10.503%	$162.8041	$162.80	$162.80	$162.80
Purchase #6	$29.58	3.524%	$30.6224	$30.62	$30.60	$30.60
Purchase #7	$72.53	4.628%	$75.8867	$75.89	$75.90	$75.90
7 purchase totals =	$759.97		$815.4068	$815.42	$815.35	$815.40