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	$68.86	8.178%	$74.4914	$74.49	$74.50	$74.50
Purchase #2	$114.45	7.477%	$123.0074	$123.01	$123.00	$123.00
Purchase #3	$190.98	9.870%	$209.8297	$209.83	$209.85	$209.80
Purchase #4	$98.84	10.604%	$109.321	$109.32	$109.30	$109.30
Purchase #5	$224.96	11.502%	$250.8349	$250.83	$250.85	$250.80
Purchase #6	$170.84	13.857%	$194.5133	$194.51	$194.50	$194.50
Purchase #7	$150.40	12.291%	$168.8857	$168.89	$168.90	$168.90
7 purchase totals =	$1,019.33		$1,130.8834	$1,130.88	$1,130.90	$1,130.80