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	$155.34	10.427%	$171.5373	$171.54	$171.55	$171.50
Purchase #2	$179.45	4.781%	$188.0295	$188.03	$188.05	$188.00
Purchase #3	$152.70	10.711%	$169.0557	$169.06	$169.05	$169.10
Purchase #4	$151.33	3.630%	$156.8233	$156.82	$156.80	$156.80
Purchase #5	$171.80	7.840%	$185.2691	$185.27	$185.25	$185.30
Purchase #6	$155.39	12.726%	$175.1649	$175.16	$175.15	$175.20
Purchase #7	$232.94	8.459%	$252.6444	$252.64	$252.65	$252.60
7 purchase totals =	$1,198.95		$1,298.5242	$1,298.52	$1,298.50	$1,298.50