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	$187.40	3.673%	$194.2832	$194.28	$194.30	$194.30
Purchase #2	$127.73	3.588%	$132.313	$132.31	$132.30	$132.30
Purchase #3	$150.70	8.105%	$162.9142	$162.91	$162.90	$162.90
Purchase #4	$231.61	3.333%	$239.3296	$239.33	$239.35	$239.30
Purchase #5	$149.62	9.722%	$164.1661	$164.17	$164.15	$164.20
Purchase #6	$133.78	8.692%	$145.4082	$145.41	$145.40	$145.40
Purchase #7	$50.72	4.157%	$52.8284	$52.83	$52.85	$52.80
7 purchase totals =	$1,031.56		$1,091.2427	$1,091.24	$1,091.25	$1,091.20