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	$20.33	6.808%	$21.7141	$21.71	$21.70	$21.70
Purchase #2	$164.28	6.640%	$175.1882	$175.19	$175.20	$175.20
Purchase #3	$194.85	10.105%	$214.5396	$214.54	$214.55	$214.50
Purchase #4	$184.93	3.461%	$191.3304	$191.33	$191.35	$191.30
Purchase #5	$124.28	6.152%	$131.9257	$131.93	$131.95	$131.90
Purchase #6	$76.29	12.235%	$85.6241	$85.62	$85.60	$85.60
Purchase #7	$240.38	13.105%	$271.8818	$271.88	$271.90	$271.90
7 purchase totals =	$1,005.34		$1,092.2039	$1,092.20	$1,092.25	$1,092.10