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	$212.29	11.801%	$237.3423	$237.34	$237.35	$237.30
Purchase #2	$199.39	4.400%	$208.1632	$208.16	$208.15	$208.20
Purchase #3	$184.72	13.352%	$209.3838	$209.38	$209.40	$209.40
Purchase #4	$222.74	6.420%	$237.0399	$237.04	$237.05	$237.00
Purchase #5	$131.69	7.331%	$141.3442	$141.34	$141.35	$141.30
Purchase #6	$158.56	9.181%	$173.1174	$173.12	$173.10	$173.10
Purchase #7	$109.90	12.169%	$123.2737	$123.27	$123.25	$123.30
7 purchase totals =	$1,219.29		$1,329.6645	$1,329.65	$1,329.65	$1,329.60