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	$31.36	4.848%	$32.8803	$32.88	$32.90	$32.90
Purchase #2	$196.31	7.208%	$210.46	$210.46	$210.45	$210.50
Purchase #3	$84.60	5.341%	$89.1185	$89.12	$89.10	$89.10
Purchase #4	$124.44	10.874%	$137.9716	$137.97	$137.95	$138.00
Purchase #5	$137.33	5.502%	$144.8859	$144.89	$144.90	$144.90
Purchase #6	$170.32	4.666%	$178.2671	$178.27	$178.25	$178.30
Purchase #7	$124.57	11.665%	$139.1011	$139.10	$139.10	$139.10
7 purchase totals =	$868.93		$932.6845	$932.69	$932.65	$932.80