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	$203.82	13.494%	$231.3235	$231.32	$231.30	$231.30
Purchase #2	$58.90	4.263%	$61.4109	$61.41	$61.40	$61.40
Purchase #3	$181.59	10.545%	$200.7387	$200.74	$200.75	$200.70
Purchase #4	$134.77	7.328%	$144.6459	$144.65	$144.65	$144.60
Purchase #5	$120.37	11.377%	$134.0645	$134.06	$134.05	$134.10
Purchase #6	$34.90	9.405%	$38.1823	$38.18	$38.20	$38.20
Purchase #7	$182.42	9.360%	$199.4945	$199.49	$199.50	$199.50
7 purchase totals =	$916.77		$1,009.8603	$1,009.85	$1,009.85	$1,009.80