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	$23.40	9.753%	$25.6822	$25.68	$25.70	$25.70
Purchase #2	$90.95	9.561%	$99.6457	$99.65	$99.65	$99.60
Purchase #3	$43.83	6.517%	$46.6864	$46.69	$46.70	$46.70
Purchase #4	$202.53	12.154%	$227.1455	$227.15	$227.15	$227.10
Purchase #5	$248.87	6.254%	$264.4343	$264.43	$264.45	$264.40
Purchase #6	$106.94	9.753%	$117.3699	$117.37	$117.35	$117.40
Purchase #7	$103.78	5.498%	$109.4858	$109.49	$109.50	$109.50
7 purchase totals =	$820.30		$890.4498	$890.46	$890.50	$890.40