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	$42.60	11.530%	$47.5118	$47.51	$47.50	$47.50
Purchase #2	$24.43	12.729%	$27.5397	$27.54	$27.55	$27.50
Purchase #3	$150.74	9.464%	$165.006	$165.01	$165.00	$165.00
Purchase #4	$219.26	3.223%	$226.3267	$226.33	$226.35	$226.30
Purchase #5	$149.49	9.755%	$164.0727	$164.07	$164.05	$164.10
Purchase #6	$74.73	11.512%	$83.3329	$83.33	$83.35	$83.30
Purchase #7	$105.56	7.506%	$113.4833	$113.48	$113.50	$113.50
7 purchase totals =	$766.81		$827.2731	$827.27	$827.30	$827.20