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	$129.46	3.615%	$134.14	$134.14	$134.15	$134.10
Purchase #2	$45.61	11.635%	$50.9167	$50.92	$50.90	$50.90
Purchase #3	$57.59	6.680%	$61.437	$61.44	$61.45	$61.40
Purchase #4	$154.37	8.737%	$167.8573	$167.86	$167.85	$167.90
Purchase #5	$115.45	11.211%	$128.3931	$128.39	$128.40	$128.40
Purchase #6	$35.96	11.172%	$39.9775	$39.98	$40.00	$40.00
Purchase #7	$102.89	3.114%	$106.094	$106.09	$106.10	$106.10
7 purchase totals =	$641.33		$688.8156	$688.82	$688.85	$688.80