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	$84.83	7.400%	$91.1074	$91.11	$91.10	$91.10
Purchase #2	$37.69	4.185%	$39.2673	$39.27	$39.25	$39.30
Purchase #3	$99.58	3.738%	$103.3023	$103.30	$103.30	$103.30
Purchase #4	$249.43	12.224%	$279.9203	$279.92	$279.90	$279.90
Purchase #5	$59.56	9.735%	$65.3582	$65.36	$65.35	$65.40
Purchase #6	$206.75	6.384%	$219.9489	$219.95	$219.95	$219.90
Purchase #7	$189.85	3.509%	$196.5118	$196.51	$196.50	$196.50
7 purchase totals =	$927.69		$995.4162	$995.42	$995.35	$995.40