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	$33.50	11.600%	$37.386	$37.39	$37.40	$37.40
Purchase #2	$17.64	5.641%	$18.6351	$18.64	$18.65	$18.60
Purchase #3	$71.88	7.439%	$77.2272	$77.23	$77.25	$77.20
Purchase #4	$225.66	9.598%	$247.3188	$247.32	$247.30	$247.30
Purchase #5	$174.46	8.172%	$188.7169	$188.72	$188.70	$188.70
Purchase #6	$163.64	10.293%	$180.4835	$180.48	$180.50	$180.50
Purchase #7	$90.91	11.597%	$101.4528	$101.45	$101.45	$101.50
7 purchase totals =	$777.69		$851.2203	$851.23	$851.25	$851.20