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	$95.45	7.350%	$102.4656	$102.47	$102.45	$102.50
Purchase #2	$141.28	8.203%	$152.8692	$152.87	$152.85	$152.90
Purchase #3	$244.80	11.482%	$272.9079	$272.91	$272.90	$272.90
Purchase #4	$164.49	8.427%	$178.3516	$178.35	$178.35	$178.40
Purchase #5	$73.59	12.847%	$83.0441	$83.04	$83.05	$83.00
Purchase #6	$53.86	12.360%	$60.5171	$60.52	$60.50	$60.50
Purchase #7	$119.67	9.757%	$131.3462	$131.35	$131.35	$131.30
7 purchase totals =	$893.14		$981.5017	$981.51	$981.45	$981.50