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	$46.49	13.284%	$52.6657	$52.67	$52.65	$52.70
Purchase #2	$248.83	8.490%	$269.9557	$269.96	$269.95	$270.00
Purchase #3	$40.62	11.649%	$45.3518	$45.35	$45.35	$45.40
Purchase #4	$240.62	6.362%	$255.9282	$255.93	$255.95	$255.90
Purchase #5	$61.25	8.107%	$66.2155	$66.22	$66.20	$66.20
Purchase #6	$152.27	10.355%	$168.0376	$168.04	$168.05	$168.00
Purchase #7	$133.47	4.579%	$139.5816	$139.58	$139.60	$139.60
7 purchase totals =	$923.55		$997.7361	$997.75	$997.75	$997.80