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	$86.53	4.112%	$90.0881	$90.09	$90.10	$90.10
Purchase #2	$247.47	11.804%	$276.6814	$276.68	$276.70	$276.70
Purchase #3	$128.65	6.501%	$137.0135	$137.01	$137.00	$137.00
Purchase #4	$161.48	12.436%	$181.5617	$181.56	$181.55	$181.60
Purchase #5	$32.91	9.740%	$36.1154	$36.12	$36.10	$36.10
Purchase #6	$39.31	5.756%	$41.5727	$41.57	$41.55	$41.60
Purchase #7	$141.48	7.455%	$152.0273	$152.03	$152.05	$152.00
7 purchase totals =	$837.83		$915.0601	$915.06	$915.05	$915.10