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	$198.76	4.819%	$208.3382	$208.34	$208.35	$208.30
Purchase #2	$79.36	5.120%	$83.4232	$83.42	$83.40	$83.40
Purchase #3	$150.97	12.336%	$169.5937	$169.59	$169.60	$169.60
Purchase #4	$145.61	9.285%	$159.1299	$159.13	$159.15	$159.10
Purchase #5	$63.65	3.870%	$66.1133	$66.11	$66.10	$66.10
Purchase #6	$52.88	9.210%	$57.7502	$57.75	$57.75	$57.80
Purchase #7	$81.38	10.427%	$89.8655	$89.87	$89.85	$89.90
7 purchase totals =	$772.61		$834.2140	$834.21	$834.20	$834.20