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	$246.73	8.826%	$268.5064	$268.51	$268.50	$268.50
Purchase #2	$100.37	11.624%	$112.037	$112.04	$112.05	$112.00
Purchase #3	$93.73	13.253%	$106.152	$106.15	$106.15	$106.20
Purchase #4	$109.65	9.139%	$119.6709	$119.67	$119.65	$119.70
Purchase #5	$101.33	10.493%	$111.9626	$111.96	$111.95	$112.00
Purchase #6	$149.88	11.440%	$167.0263	$167.03	$167.05	$167.00
Purchase #7	$52.74	9.758%	$57.8864	$57.89	$57.90	$57.90
7 purchase totals =	$854.43		$943.2416	$943.25	$943.25	$943.30