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	$59.57	12.718%	$67.1461	$67.15	$67.15	$67.10
Purchase #2	$35.80	10.222%	$39.4595	$39.46	$39.45	$39.50
Purchase #3	$57.46	12.123%	$64.4259	$64.43	$64.45	$64.40
Purchase #4	$117.49	10.606%	$129.951	$129.95	$129.95	$130.00
Purchase #5	$217.96	3.871%	$226.3972	$226.40	$226.40	$226.40
Purchase #6	$40.52	4.436%	$42.3175	$42.32	$42.30	$42.30
Purchase #7	$38.67	3.871%	$40.1669	$40.17	$40.15	$40.20
7 purchase totals =	$567.47		$609.8641	$609.88	$609.85	$609.90