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	$143.34	5.836%	$151.7053	$151.71	$151.70	$151.70
Purchase #2	$19.44	11.592%	$21.6935	$21.69	$21.70	$21.70
Purchase #3	$34.72	13.336%	$39.3503	$39.35	$39.35	$39.40
Purchase #4	$170.34	10.113%	$187.5665	$187.57	$187.55	$187.60
Purchase #5	$31.26	3.113%	$32.2331	$32.23	$32.25	$32.20
Purchase #6	$186.82	7.366%	$200.5812	$200.58	$200.60	$200.60
Purchase #7	$35.32	5.704%	$37.3347	$37.33	$37.35	$37.30
7 purchase totals =	$621.24		$670.4646	$670.46	$670.50	$670.50