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	$20.99	8.840%	$22.8455	$22.85	$22.85	$22.80
Purchase #2	$100.94	4.527%	$105.5096	$105.51	$105.50	$105.50
Purchase #3	$130.40	5.760%	$137.911	$137.91	$137.90	$137.90
Purchase #4	$201.46	10.600%	$222.8148	$222.81	$222.80	$222.80
Purchase #5	$204.81	3.156%	$211.2738	$211.27	$211.25	$211.30
Purchase #6	$177.33	6.717%	$189.2413	$189.24	$189.25	$189.20
Purchase #7	$168.43	12.168%	$188.9246	$188.92	$188.90	$188.90
7 purchase totals =	$1,004.36		$1,078.5206	$1,078.51	$1,078.45	$1,078.40