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	$243.42	9.610%	$266.8127	$266.81	$266.80	$266.80
Purchase #2	$181.77	5.834%	$192.3745	$192.37	$192.35	$192.40
Purchase #3	$40.89	5.399%	$43.0977	$43.10	$43.10	$43.10
Purchase #4	$144.41	9.591%	$158.2604	$158.26	$158.25	$158.30
Purchase #5	$216.37	10.639%	$239.3896	$239.39	$239.40	$239.40
Purchase #6	$77.38	7.233%	$82.9769	$82.98	$83.00	$83.00
Purchase #7	$100.51	6.787%	$107.3316	$107.33	$107.35	$107.30
7 purchase totals =	$1,004.75		$1,090.2434	$1,090.24	$1,090.25	$1,090.30