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	$175.39	7.763%	$189.0055	$189.01	$189.00	$189.00
Purchase #2	$104.86	6.697%	$111.8825	$111.88	$111.90	$111.90
Purchase #3	$59.72	9.275%	$65.259	$65.26	$65.25	$65.30
Purchase #4	$109.67	3.289%	$113.277	$113.28	$113.30	$113.30
Purchase #5	$108.81	3.818%	$112.9644	$112.96	$112.95	$113.00
Purchase #6	$32.55	12.553%	$36.636	$36.64	$36.65	$36.60
Purchase #7	$51.56	4.513%	$53.8869	$53.89	$53.90	$53.90
7 purchase totals =	$642.56		$682.9113	$682.92	$682.95	$683.00