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	$123.87	8.321%	$134.1772	$134.18	$134.20	$134.20
Purchase #2	$223.26	13.374%	$253.1188	$253.12	$253.10	$253.10
Purchase #3	$118.77	8.216%	$128.5281	$128.53	$128.55	$128.50
Purchase #4	$213.95	9.152%	$233.5307	$233.53	$233.55	$233.50
Purchase #5	$103.95	5.695%	$109.87	$109.87	$109.85	$109.90
Purchase #6	$115.54	10.296%	$127.436	$127.44	$127.45	$127.40
Purchase #7	$19.39	9.503%	$21.2326	$21.23	$21.25	$21.20
7 purchase totals =	$918.73		$1,007.8934	$1,007.90	$1,007.95	$1,007.80