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	$34.61	7.842%	$37.3241	$37.32	$37.30	$37.30
Purchase #2	$35.97	8.239%	$38.9336	$38.93	$38.95	$38.90
Purchase #3	$176.44	11.326%	$196.4236	$196.42	$196.40	$196.40
Purchase #4	$127.86	9.181%	$139.5988	$139.60	$139.60	$139.60
Purchase #5	$11.52	4.744%	$12.0665	$12.07	$12.05	$12.10
Purchase #6	$31.53	4.633%	$32.9908	$32.99	$33.00	$33.00
Purchase #7	$42.41	7.393%	$45.5454	$45.55	$45.55	$45.50
7 purchase totals =	$460.34		$502.8828	$502.88	$502.85	$502.80