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	$19.35	9.775%	$21.2415	$21.24	$21.25	$21.20
Purchase #2	$38.38	7.412%	$41.2247	$41.22	$41.20	$41.20
Purchase #3	$121.29	5.267%	$127.6783	$127.68	$127.70	$127.70
Purchase #4	$188.71	7.264%	$202.4179	$202.42	$202.40	$202.40
Purchase #5	$54.72	9.447%	$59.8894	$59.89	$59.90	$59.90
Purchase #6	$85.35	5.531%	$90.0707	$90.07	$90.05	$90.10
Purchase #7	$123.57	12.824%	$139.4166	$139.42	$139.40	$139.40
7 purchase totals =	$631.37		$681.9391	$681.94	$681.90	$681.90