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	$229.66	12.815%	$259.0909	$259.09	$259.10	$259.10
Purchase #2	$94.64	11.867%	$105.8709	$105.87	$105.85	$105.90
Purchase #3	$87.31	4.673%	$91.39	$91.39	$91.40	$91.40
Purchase #4	$211.96	9.767%	$232.6621	$232.66	$232.65	$232.70
Purchase #5	$28.27	12.670%	$31.8518	$31.85	$31.85	$31.90
Purchase #6	$233.43	10.330%	$257.5433	$257.54	$257.55	$257.50
Purchase #7	$131.61	10.817%	$145.8463	$145.85	$145.85	$145.80
7 purchase totals =	$1,016.88		$1,124.2553	$1,124.25	$1,124.25	$1,124.30