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	$80.81	3.739%	$83.8315	$83.83	$83.85	$83.80
Purchase #2	$98.76	12.344%	$110.9509	$110.95	$110.95	$111.00
Purchase #3	$135.29	4.516%	$141.3997	$141.40	$141.40	$141.40
Purchase #4	$139.89	8.642%	$151.9793	$151.98	$152.00	$152.00
Purchase #5	$7.97	10.349%	$8.7948	$8.79	$8.80	$8.80
Purchase #6	$98.37	13.551%	$111.7001	$111.70	$111.70	$111.70
Purchase #7	$168.34	5.800%	$178.1037	$178.10	$178.10	$178.10
7 purchase totals =	$729.43		$786.7600	$786.75	$786.80	$786.80