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	$244.94	10.819%	$271.4401	$271.44	$271.45	$271.40
Purchase #2	$24.74	4.245%	$25.7902	$25.79	$25.80	$25.80
Purchase #3	$96.51	4.589%	$100.9388	$100.94	$100.95	$100.90
Purchase #4	$123.56	12.586%	$139.1113	$139.11	$139.10	$139.10
Purchase #5	$226.32	4.452%	$236.3958	$236.40	$236.40	$236.40
Purchase #6	$103.71	12.667%	$116.8469	$116.85	$116.85	$116.80
Purchase #7	$131.53	12.357%	$147.7832	$147.78	$147.80	$147.80
7 purchase totals =	$951.31		$1,038.3063	$1,038.31	$1,038.35	$1,038.20