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	$242.28	12.810%	$273.3161	$273.32	$273.30	$273.30
Purchase #2	$24.98	3.583%	$25.875	$25.88	$25.90	$25.90
Purchase #3	$185.90	5.522%	$196.1654	$196.17	$196.15	$196.20
Purchase #4	$248.50	10.856%	$275.4772	$275.48	$275.50	$275.50
Purchase #5	$141.46	3.842%	$146.8949	$146.89	$146.90	$146.90
Purchase #6	$142.93	12.465%	$160.7462	$160.75	$160.75	$160.70
Purchase #7	$148.47	5.329%	$156.382	$156.38	$156.40	$156.40
7 purchase totals =	$1,134.52		$1,234.8568	$1,234.87	$1,234.90	$1,234.90