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	$13.80	12.511%	$15.5265	$15.53	$15.55	$15.50
Purchase #2	$148.85	4.526%	$155.587	$155.59	$155.60	$155.60
Purchase #3	$86.25	4.185%	$89.8596	$89.86	$89.85	$89.90
Purchase #4	$218.98	12.313%	$245.943	$245.94	$245.95	$245.90
Purchase #5	$141.70	10.245%	$156.2172	$156.22	$156.20	$156.20
Purchase #6	$115.29	7.136%	$123.5171	$123.52	$123.50	$123.50
Purchase #7	$236.26	11.203%	$262.7282	$262.73	$262.75	$262.70
7 purchase totals =	$961.13		$1,049.3786	$1,049.39	$1,049.40	$1,049.30