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	$140.25	4.436%	$146.4715	$146.47	$146.45	$146.50
Purchase #2	$51.38	3.475%	$53.1655	$53.17	$53.15	$53.20
Purchase #3	$59.67	13.504%	$67.7278	$67.73	$67.75	$67.70
Purchase #4	$72.80	3.707%	$75.4987	$75.50	$75.50	$75.50
Purchase #5	$104.96	4.295%	$109.468	$109.47	$109.45	$109.50
Purchase #6	$24.65	10.841%	$27.3223	$27.32	$27.30	$27.30
Purchase #7	$166.43	7.605%	$179.087	$179.09	$179.10	$179.10
7 purchase totals =	$620.14		$658.7408	$658.75	$658.70	$658.80