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	$223.74	6.505%	$238.2943	$238.29	$238.30	$238.30
Purchase #2	$209.40	4.590%	$219.0115	$219.01	$219.00	$219.00
Purchase #3	$60.32	5.296%	$63.5145	$63.51	$63.50	$63.50
Purchase #4	$6.34	13.756%	$7.2121	$7.21	$7.20	$7.20
Purchase #5	$34.40	7.240%	$36.8906	$36.89	$36.90	$36.90
Purchase #6	$31.25	11.608%	$34.8775	$34.88	$34.90	$34.90
Purchase #7	$19.59	9.856%	$21.5208	$21.52	$21.50	$21.50
7 purchase totals =	$585.04		$621.3213	$621.31	$621.30	$621.30