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	$85.89	12.396%	$96.5369	$96.54	$96.55	$96.50
Purchase #2	$93.48	10.324%	$103.1309	$103.13	$103.15	$103.10
Purchase #3	$78.83	4.648%	$82.494	$82.49	$82.50	$82.50
Purchase #4	$40.95	10.127%	$45.097	$45.10	$45.10	$45.10
Purchase #5	$7.51	8.852%	$8.1748	$8.17	$8.15	$8.20
Purchase #6	$110.39	6.797%	$117.8932	$117.89	$117.90	$117.90
Purchase #7	$170.63	11.773%	$190.7183	$190.72	$190.70	$190.70
7 purchase totals =	$587.68		$644.0451	$644.04	$644.05	$644.00