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	$123.88	10.854%	$137.3259	$137.33	$137.35	$137.30
Purchase #2	$88.88	8.160%	$96.1326	$96.13	$96.15	$96.10
Purchase #3	$106.67	11.818%	$119.2763	$119.28	$119.30	$119.30
Purchase #4	$229.38	13.356%	$260.016	$260.02	$260.00	$260.00
Purchase #5	$145.62	3.770%	$151.1099	$151.11	$151.10	$151.10
Purchase #6	$143.29	12.447%	$161.1253	$161.13	$161.15	$161.10
Purchase #7	$100.30	12.521%	$112.8586	$112.86	$112.85	$112.90
7 purchase totals =	$938.02		$1,037.8446	$1,037.86	$1,037.90	$1,037.80