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	$37.84	4.114%	$39.3967	$39.40	$39.40	$39.40
Purchase #2	$236.69	5.165%	$248.915	$248.92	$248.90	$248.90
Purchase #3	$125.77	13.218%	$142.3943	$142.39	$142.40	$142.40
Purchase #4	$54.97	11.605%	$61.3493	$61.35	$61.35	$61.30
Purchase #5	$228.84	9.465%	$250.4997	$250.50	$250.50	$250.50
Purchase #6	$62.25	12.268%	$69.8868	$69.89	$69.90	$69.90
Purchase #7	$144.91	4.512%	$151.4483	$151.45	$151.45	$151.40
7 purchase totals =	$891.27		$963.8901	$963.90	$963.90	$963.80