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	$141.72	4.817%	$148.5467	$148.55	$148.55	$148.50
Purchase #2	$171.50	10.632%	$189.7339	$189.73	$189.75	$189.70
Purchase #3	$172.47	11.440%	$192.2006	$192.20	$192.20	$192.20
Purchase #4	$155.70	4.618%	$162.8902	$162.89	$162.90	$162.90
Purchase #5	$83.91	8.598%	$91.1246	$91.12	$91.10	$91.10
Purchase #6	$230.89	8.221%	$249.8715	$249.87	$249.85	$249.90
Purchase #7	$39.53	7.828%	$42.6244	$42.62	$42.60	$42.60
7 purchase totals =	$995.72		$1,076.9919	$1,076.98	$1,076.95	$1,076.90