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	$140.85	6.588%	$150.1292	$150.13	$150.15	$150.10
Purchase #2	$170.52	8.448%	$184.9255	$184.93	$184.95	$184.90
Purchase #3	$222.87	10.539%	$246.3583	$246.36	$246.35	$246.40
Purchase #4	$90.39	9.356%	$98.8469	$98.85	$98.85	$98.80
Purchase #5	$100.58	10.426%	$111.0665	$111.07	$111.05	$111.10
Purchase #6	$242.75	10.423%	$268.0518	$268.05	$268.05	$268.10
Purchase #7	$58.92	9.395%	$64.4555	$64.46	$64.45	$64.50
7 purchase totals =	$1,026.88		$1,123.8337	$1,123.85	$1,123.85	$1,123.90