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	$243.53	9.841%	$267.4958	$267.50	$267.50	$267.50
Purchase #2	$17.73	4.413%	$18.5124	$18.51	$18.50	$18.50
Purchase #3	$61.37	11.172%	$68.2263	$68.23	$68.25	$68.20
Purchase #4	$231.56	3.763%	$240.2736	$240.27	$240.25	$240.30
Purchase #5	$53.78	11.665%	$60.0534	$60.05	$60.05	$60.10
Purchase #6	$86.93	4.582%	$90.9131	$90.91	$90.90	$90.90
Purchase #7	$223.52	3.520%	$231.3879	$231.39	$231.40	$231.40
7 purchase totals =	$918.42		$976.8625	$976.86	$976.85	$976.90