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	$242.96	7.723%	$261.7238	$261.72	$261.70	$261.70
Purchase #2	$180.38	3.550%	$186.7835	$186.78	$186.80	$186.80
Purchase #3	$90.71	10.334%	$100.084	$100.08	$100.10	$100.10
Purchase #4	$34.34	3.640%	$35.59	$35.59	$35.60	$35.60
Purchase #5	$12.50	11.742%	$13.9678	$13.97	$13.95	$14.00
Purchase #6	$59.59	9.687%	$65.3625	$65.36	$65.35	$65.40
Purchase #7	$117.79	11.133%	$130.9036	$130.90	$130.90	$130.90
7 purchase totals =	$738.27		$794.4152	$794.40	$794.40	$794.50