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	$105.61	13.240%	$119.5928	$119.59	$119.60	$119.60
Purchase #2	$229.37	12.140%	$257.2155	$257.22	$257.20	$257.20
Purchase #3	$217.32	12.441%	$244.3568	$244.36	$244.35	$244.40
Purchase #4	$42.62	6.546%	$45.4099	$45.41	$45.40	$45.40
Purchase #5	$11.92	11.453%	$13.2852	$13.29	$13.30	$13.30
Purchase #6	$123.78	8.208%	$133.9399	$133.94	$133.95	$133.90
Purchase #7	$58.42	5.323%	$61.5297	$61.53	$61.55	$61.50
7 purchase totals =	$789.04		$875.3298	$875.34	$875.35	$875.30