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	$21.48	3.685%	$22.2715	$22.27	$22.25	$22.30
Purchase #2	$178.98	6.240%	$190.1484	$190.15	$190.15	$190.10
Purchase #3	$123.67	7.195%	$132.5681	$132.57	$132.55	$132.60
Purchase #4	$23.40	8.484%	$25.3853	$25.39	$25.40	$25.40
Purchase #5	$98.95	11.567%	$110.3955	$110.40	$110.40	$110.40
Purchase #6	$138.49	12.828%	$156.2555	$156.26	$156.25	$156.30
Purchase #7	$175.56	11.772%	$196.2269	$196.23	$196.25	$196.20
7 purchase totals =	$760.53		$833.2512	$833.27	$833.25	$833.30