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	$90.69	9.727%	$99.5114	$99.51	$99.50	$99.50
Purchase #2	$224.96	12.625%	$253.3612	$253.36	$253.35	$253.40
Purchase #3	$47.96	13.654%	$54.5085	$54.51	$54.50	$54.50
Purchase #4	$161.88	4.543%	$169.2342	$169.23	$169.25	$169.20
Purchase #5	$99.74	8.253%	$107.9715	$107.97	$107.95	$108.00
Purchase #6	$29.35	11.161%	$32.6258	$32.63	$32.65	$32.60
Purchase #7	$196.79	12.651%	$221.6859	$221.69	$221.70	$221.70
7 purchase totals =	$851.37		$938.8985	$938.90	$938.90	$938.90