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	$14.26	8.856%	$15.5229	$15.52	$15.50	$15.50
Purchase #2	$82.61	11.224%	$91.8821	$91.88	$91.90	$91.90
Purchase #3	$238.34	12.535%	$268.2159	$268.22	$268.20	$268.20
Purchase #4	$39.29	13.304%	$44.5171	$44.52	$44.50	$44.50
Purchase #5	$234.61	13.371%	$265.9797	$265.98	$266.00	$266.00
Purchase #6	$246.32	5.323%	$259.4316	$259.43	$259.45	$259.40
Purchase #7	$146.31	12.349%	$164.3778	$164.38	$164.40	$164.40
7 purchase totals =	$1,001.74		$1,109.9271	$1,109.93	$1,109.95	$1,109.90