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	$150.31	3.258%	$155.2071	$155.21	$155.20	$155.20
Purchase #2	$179.86	8.212%	$194.6301	$194.63	$194.65	$194.60
Purchase #3	$109.27	4.365%	$114.0396	$114.04	$114.05	$114.00
Purchase #4	$100.41	4.138%	$104.565	$104.57	$104.55	$104.60
Purchase #5	$202.63	11.209%	$225.3428	$225.34	$225.35	$225.30
Purchase #6	$123.28	6.735%	$131.5829	$131.58	$131.60	$131.60
Purchase #7	$130.52	6.771%	$139.3575	$139.36	$139.35	$139.40
7 purchase totals =	$996.28		$1,064.7250	$1,064.73	$1,064.75	$1,064.70