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	$81.32	11.353%	$90.5523	$90.55	$90.55	$90.60
Purchase #2	$129.76	10.218%	$143.0189	$143.02	$143.00	$143.00
Purchase #3	$223.61	13.708%	$254.2625	$254.26	$254.25	$254.30
Purchase #4	$153.94	7.716%	$165.818	$165.82	$165.80	$165.80
Purchase #5	$33.35	9.380%	$36.4782	$36.48	$36.50	$36.50
Purchase #6	$80.66	3.471%	$83.4597	$83.46	$83.45	$83.50
Purchase #7	$186.52	9.438%	$204.1238	$204.12	$204.10	$204.10
7 purchase totals =	$889.16		$977.7134	$977.71	$977.65	$977.80