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	$26.68	3.801%	$27.6941	$27.69	$27.70	$27.70
Purchase #2	$40.27	4.641%	$42.1389	$42.14	$42.15	$42.10
Purchase #3	$46.51	13.372%	$52.7293	$52.73	$52.75	$52.70
Purchase #4	$172.89	9.433%	$189.1987	$189.20	$189.20	$189.20
Purchase #5	$168.61	9.722%	$185.0023	$185.00	$185.00	$185.00
Purchase #6	$156.53	3.110%	$161.3981	$161.40	$161.40	$161.40
Purchase #7	$170.51	11.801%	$190.6319	$190.63	$190.65	$190.60
7 purchase totals =	$782.00		$848.7933	$848.79	$848.85	$848.70