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	$247.67	10.649%	$274.0444	$274.04	$274.05	$274.00
Purchase #2	$73.81	11.666%	$82.4207	$82.42	$82.40	$82.40
Purchase #3	$203.64	10.644%	$225.3154	$225.32	$225.30	$225.30
Purchase #4	$123.31	12.857%	$139.164	$139.16	$139.15	$139.20
Purchase #5	$42.97	11.811%	$48.0452	$48.05	$48.05	$48.00
Purchase #6	$68.80	6.348%	$73.1674	$73.17	$73.15	$73.20
Purchase #7	$83.77	9.614%	$91.8236	$91.82	$91.80	$91.80
7 purchase totals =	$843.97		$933.9807	$933.98	$933.90	$933.90