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	$65.72	4.806%	$68.8785	$68.88	$68.90	$68.90
Purchase #2	$143.61	8.853%	$156.3238	$156.32	$156.30	$156.30
Purchase #3	$39.46	7.786%	$42.5324	$42.53	$42.55	$42.50
Purchase #4	$59.74	12.800%	$67.3867	$67.39	$67.40	$67.40
Purchase #5	$27.35	3.160%	$28.2143	$28.21	$28.20	$28.20
Purchase #6	$41.77	10.700%	$46.2394	$46.24	$46.25	$46.20
Purchase #7	$163.38	13.406%	$185.2827	$185.28	$185.30	$185.30
7 purchase totals =	$541.03		$594.8578	$594.85	$594.90	$594.80