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	$91.72	12.728%	$103.3941	$103.39	$103.40	$103.40
Purchase #2	$86.72	10.604%	$95.9158	$95.92	$95.90	$95.90
Purchase #3	$122.33	9.856%	$134.3868	$134.39	$134.40	$134.40
Purchase #4	$200.94	4.147%	$209.273	$209.27	$209.25	$209.30
Purchase #5	$63.29	12.430%	$71.1569	$71.16	$71.15	$71.20
Purchase #6	$66.42	9.113%	$72.4729	$72.47	$72.45	$72.50
Purchase #7	$212.64	11.653%	$237.4189	$237.42	$237.40	$237.40
7 purchase totals =	$844.06		$924.0184	$924.02	$923.95	$924.10