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	$161.46	13.259%	$182.868	$182.87	$182.85	$182.90
Purchase #2	$249.72	10.633%	$276.2727	$276.27	$276.25	$276.30
Purchase #3	$191.61	4.384%	$200.0102	$200.01	$200.00	$200.00
Purchase #4	$62.25	3.353%	$64.3372	$64.34	$64.35	$64.30
Purchase #5	$36.96	9.780%	$40.5747	$40.57	$40.55	$40.60
Purchase #6	$35.62	10.600%	$39.3957	$39.40	$39.40	$39.40
Purchase #7	$168.50	13.184%	$190.715	$190.72	$190.70	$190.70
7 purchase totals =	$906.12		$994.1735	$994.18	$994.10	$994.20