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	$217.43	12.763%	$245.1806	$245.18	$245.20	$245.20
Purchase #2	$88.28	11.522%	$98.4516	$98.45	$98.45	$98.50
Purchase #3	$161.69	4.233%	$168.5343	$168.53	$168.55	$168.50
Purchase #4	$39.56	8.317%	$42.8502	$42.85	$42.85	$42.90
Purchase #5	$185.74	5.234%	$195.4616	$195.46	$195.45	$195.50
Purchase #6	$33.48	10.781%	$37.0895	$37.09	$37.10	$37.10
Purchase #7	$234.94	7.693%	$253.0139	$253.01	$253.00	$253.00
7 purchase totals =	$961.12		$1,040.5817	$1,040.57	$1,040.60	$1,040.70