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	$111.44	13.283%	$126.2426	$126.24	$126.25	$126.20
Purchase #2	$59.78	10.122%	$65.8309	$65.83	$65.85	$65.80
Purchase #3	$242.56	11.220%	$269.7752	$269.78	$269.80	$269.80
Purchase #4	$137.89	3.407%	$142.5879	$142.59	$142.60	$142.60
Purchase #5	$156.98	6.723%	$167.5338	$167.53	$167.55	$167.50
Purchase #6	$201.55	4.743%	$211.1095	$211.11	$211.10	$211.10
Purchase #7	$13.89	6.531%	$14.7972	$14.80	$14.80	$14.80
7 purchase totals =	$924.09		$997.8771	$997.88	$997.95	$997.80