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	$167.61	10.786%	$185.6884	$185.69	$185.70	$185.70
Purchase #2	$51.39	5.334%	$54.1311	$54.13	$54.15	$54.10
Purchase #3	$57.44	12.301%	$64.5057	$64.51	$64.50	$64.50
Purchase #4	$100.57	9.735%	$110.3605	$110.36	$110.35	$110.40
Purchase #5	$50.70	11.455%	$56.5077	$56.51	$56.50	$56.50
Purchase #6	$49.89	7.182%	$53.4731	$53.47	$53.45	$53.50
Purchase #7	$109.41	11.318%	$121.793	$121.79	$121.80	$121.80
7 purchase totals =	$587.01		$646.4595	$646.46	$646.45	$646.50