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	$128.59	10.290%	$141.8219	$141.82	$141.80	$141.80
Purchase #2	$207.84	9.869%	$228.3517	$228.35	$228.35	$228.40
Purchase #3	$64.69	4.772%	$67.777	$67.78	$67.80	$67.80
Purchase #4	$70.71	12.483%	$79.5367	$79.54	$79.55	$79.50
Purchase #5	$151.31	4.547%	$158.1901	$158.19	$158.20	$158.20
Purchase #6	$105.28	6.633%	$112.2632	$112.26	$112.25	$112.30
Purchase #7	$69.75	12.164%	$78.2344	$78.23	$78.25	$78.20
7 purchase totals =	$798.17		$866.1750	$866.17	$866.20	$866.20