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	$180.72	4.276%	$188.4476	$188.45	$188.45	$188.40
Purchase #2	$216.36	5.354%	$227.9439	$227.94	$227.95	$227.90
Purchase #3	$250.83	5.854%	$265.5136	$265.51	$265.50	$265.50
Purchase #4	$219.89	8.581%	$238.7588	$238.76	$238.75	$238.80
Purchase #5	$155.25	12.373%	$174.4591	$174.46	$174.45	$174.50
Purchase #6	$34.70	10.381%	$38.3022	$38.30	$38.30	$38.30
Purchase #7	$76.27	11.579%	$85.1013	$85.10	$85.10	$85.10
7 purchase totals =	$1,134.02		$1,218.5265	$1,218.52	$1,218.50	$1,218.50