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	$137.40	6.646%	$146.5316	$146.53	$146.55	$146.50
Purchase #2	$59.58	12.699%	$67.1461	$67.15	$67.15	$67.10
Purchase #3	$213.94	9.788%	$234.8804	$234.88	$234.90	$234.90
Purchase #4	$249.56	5.541%	$263.3881	$263.39	$263.40	$263.40
Purchase #5	$148.52	12.766%	$167.4801	$167.48	$167.50	$167.50
Purchase #6	$162.26	4.363%	$169.3394	$169.34	$169.35	$169.30
Purchase #7	$62.82	7.822%	$67.7338	$67.73	$67.75	$67.70
7 purchase totals =	$1,034.08		$1,116.4995	$1,116.50	$1,116.60	$1,116.40