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	$129.52	5.128%	$136.1618	$136.16	$136.15	$136.20
Purchase #2	$78.58	9.221%	$85.8259	$85.83	$85.85	$85.80
Purchase #3	$77.89	6.389%	$82.8664	$82.87	$82.85	$82.90
Purchase #4	$29.46	9.342%	$32.2122	$32.21	$32.20	$32.20
Purchase #5	$103.32	11.245%	$114.9383	$114.94	$114.95	$114.90
Purchase #6	$65.59	13.311%	$74.3207	$74.32	$74.30	$74.30
Purchase #7	$219.36	6.858%	$234.4037	$234.40	$234.40	$234.40
7 purchase totals =	$703.72		$760.7290	$760.73	$760.70	$760.70