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	$11.39	13.287%	$12.9034	$12.90	$12.90	$12.90
Purchase #2	$99.82	3.481%	$103.2947	$103.29	$103.30	$103.30
Purchase #3	$169.42	13.219%	$191.8156	$191.82	$191.80	$191.80
Purchase #4	$239.66	13.664%	$272.4071	$272.41	$272.40	$272.40
Purchase #5	$81.26	6.166%	$86.2705	$86.27	$86.25	$86.30
Purchase #6	$180.58	9.776%	$198.2335	$198.23	$198.25	$198.20
Purchase #7	$107.54	8.403%	$116.5766	$116.58	$116.60	$116.60
7 purchase totals =	$889.67		$981.5014	$981.50	$981.50	$981.50