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	$182.83	12.217%	$205.1663	$205.17	$205.15	$205.20
Purchase #2	$223.54	3.644%	$231.6858	$231.69	$231.70	$231.70
Purchase #3	$153.56	5.548%	$162.0795	$162.08	$162.10	$162.10
Purchase #4	$165.56	5.258%	$174.2651	$174.27	$174.25	$174.30
Purchase #5	$49.64	12.736%	$55.9622	$55.96	$55.95	$56.00
Purchase #6	$215.27	7.488%	$231.3894	$231.39	$231.40	$231.40
Purchase #7	$27.35	8.868%	$29.7754	$29.78	$29.80	$29.80
7 purchase totals =	$1,017.75		$1,090.3237	$1,090.34	$1,090.35	$1,090.50