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	$239.90	8.621%	$260.5818	$260.58	$260.60	$260.60
Purchase #2	$189.89	5.560%	$200.4479	$200.45	$200.45	$200.40
Purchase #3	$116.82	10.337%	$128.8957	$128.90	$128.90	$128.90
Purchase #4	$34.40	3.672%	$35.6632	$35.66	$35.65	$35.70
Purchase #5	$101.31	12.844%	$114.3223	$114.32	$114.30	$114.30
Purchase #6	$133.85	6.664%	$142.7698	$142.77	$142.75	$142.80
Purchase #7	$158.78	5.767%	$167.9368	$167.94	$167.95	$167.90
7 purchase totals =	$974.95		$1,050.6175	$1,050.62	$1,050.60	$1,050.60