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	$121.56	5.138%	$127.8058	$127.81	$127.80	$127.80
Purchase #2	$193.64	13.865%	$220.4882	$220.49	$220.50	$220.50
Purchase #3	$224.73	4.630%	$235.135	$235.14	$235.15	$235.10
Purchase #4	$119.98	6.443%	$127.7103	$127.71	$127.70	$127.70
Purchase #5	$104.55	3.381%	$108.0848	$108.08	$108.10	$108.10
Purchase #6	$112.79	3.575%	$116.8222	$116.82	$116.80	$116.80
Purchase #7	$37.61	4.405%	$39.2667	$39.27	$39.25	$39.30
7 purchase totals =	$914.86		$975.3130	$975.32	$975.30	$975.30