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	$38.58	9.870%	$42.3878	$42.39	$42.40	$42.40
Purchase #2	$106.43	7.555%	$114.4708	$114.47	$114.45	$114.50
Purchase #3	$6.91	4.738%	$7.2374	$7.24	$7.25	$7.20
Purchase #4	$87.55	6.227%	$93.0017	$93.00	$93.00	$93.00
Purchase #5	$59.96	3.435%	$62.0196	$62.02	$62.00	$62.00
Purchase #6	$38.83	4.297%	$40.4985	$40.50	$40.50	$40.50
Purchase #7	$133.44	4.285%	$139.1579	$139.16	$139.15	$139.20
7 purchase totals =	$471.70		$498.7737	$498.78	$498.75	$498.80