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	$159.89	5.177%	$168.1675	$168.17	$168.15	$168.20
Purchase #2	$191.72	9.523%	$209.9775	$209.98	$210.00	$210.00
Purchase #3	$140.58	7.749%	$151.4735	$151.47	$151.45	$151.50
Purchase #4	$110.96	11.704%	$123.9468	$123.95	$123.95	$123.90
Purchase #5	$35.62	7.520%	$38.2986	$38.30	$38.30	$38.30
Purchase #6	$59.93	9.377%	$65.5496	$65.55	$65.55	$65.50
Purchase #7	$177.39	11.753%	$198.2386	$198.24	$198.25	$198.20
7 purchase totals =	$876.09		$955.6521	$955.66	$955.65	$955.60