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	$121.42	4.851%	$127.3101	$127.31	$127.30	$127.30
Purchase #2	$204.79	9.537%	$224.3208	$224.32	$224.30	$224.30
Purchase #3	$227.73	5.789%	$240.9133	$240.91	$240.90	$240.90
Purchase #4	$102.52	9.353%	$112.1087	$112.11	$112.10	$112.10
Purchase #5	$150.90	4.290%	$157.3736	$157.37	$157.35	$157.40
Purchase #6	$203.55	6.423%	$216.624	$216.62	$216.60	$216.60
Purchase #7	$172.78	13.542%	$196.1779	$196.18	$196.20	$196.20
7 purchase totals =	$1,183.69		$1,274.8284	$1,274.82	$1,274.75	$1,274.80