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	$76.88	7.201%	$82.4161	$82.42	$82.40	$82.40
Purchase #2	$38.44	9.562%	$42.1156	$42.12	$42.10	$42.10
Purchase #3	$133.76	7.258%	$143.4683	$143.47	$143.45	$143.50
Purchase #4	$13.97	10.348%	$15.4156	$15.42	$15.40	$15.40
Purchase #5	$110.87	7.285%	$118.9469	$118.95	$118.95	$118.90
Purchase #6	$205.86	9.811%	$226.0569	$226.06	$226.05	$226.10
Purchase #7	$123.56	11.870%	$138.2266	$138.23	$138.25	$138.20
7 purchase totals =	$703.34		$766.6460	$766.67	$766.60	$766.60