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	$48.48	3.850%	$50.3465	$50.35	$50.35	$50.30
Purchase #2	$172.95	7.790%	$186.4228	$186.42	$186.40	$186.40
Purchase #3	$180.51	6.602%	$192.4273	$192.43	$192.45	$192.40
Purchase #4	$232.68	11.809%	$260.1572	$260.16	$260.15	$260.20
Purchase #5	$219.78	6.515%	$234.0987	$234.10	$234.10	$234.10
Purchase #6	$83.25	9.179%	$90.8915	$90.89	$90.90	$90.90
Purchase #7	$38.78	4.227%	$40.4192	$40.42	$40.40	$40.40
7 purchase totals =	$976.43		$1,054.7632	$1,054.77	$1,054.75	$1,054.70