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	$124.80	9.371%	$136.495	$136.50	$136.50	$136.50
Purchase #2	$124.55	13.191%	$140.9794	$140.98	$141.00	$141.00
Purchase #3	$106.39	4.803%	$111.4999	$111.50	$111.50	$111.50
Purchase #4	$13.38	11.199%	$14.8784	$14.88	$14.90	$14.90
Purchase #5	$201.68	13.348%	$228.6002	$228.60	$228.60	$228.60
Purchase #6	$95.96	3.142%	$98.9751	$98.98	$99.00	$99.00
Purchase #7	$174.68	3.658%	$181.0698	$181.07	$181.05	$181.10
7 purchase totals =	$841.44		$912.4978	$912.51	$912.55	$912.60