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	$39.71	9.269%	$43.3907	$43.39	$43.40	$43.40
Purchase #2	$10.95	10.430%	$12.0921	$12.09	$12.10	$12.10
Purchase #3	$155.31	10.402%	$171.4653	$171.47	$171.45	$171.50
Purchase #4	$51.32	9.760%	$56.3288	$56.33	$56.35	$56.30
Purchase #5	$116.33	6.374%	$123.7449	$123.74	$123.75	$123.70
Purchase #6	$190.56	4.477%	$199.0914	$199.09	$199.10	$199.10
Purchase #7	$55.61	7.747%	$59.9181	$59.92	$59.90	$59.90
7 purchase totals =	$619.79		$666.0313	$666.03	$666.05	$666.00