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	$54.94	4.804%	$57.5793	$57.58	$57.60	$57.60
Purchase #2	$158.71	6.189%	$168.5326	$168.53	$168.55	$168.50
Purchase #3	$72.82	6.456%	$77.5213	$77.52	$77.50	$77.50
Purchase #4	$32.86	12.330%	$36.9116	$36.91	$36.90	$36.90
Purchase #5	$220.96	10.150%	$243.3874	$243.39	$243.40	$243.40
Purchase #6	$66.59	11.316%	$74.1253	$74.13	$74.15	$74.10
Purchase #7	$67.71	8.375%	$73.3807	$73.38	$73.40	$73.40
7 purchase totals =	$674.59		$731.4382	$731.44	$731.50	$731.40