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	$140.76	6.788%	$150.3148	$150.31	$150.30	$150.30
Purchase #2	$237.73	11.570%	$265.2354	$265.24	$265.25	$265.20
Purchase #3	$144.83	9.706%	$158.8872	$158.89	$158.90	$158.90
Purchase #4	$156.25	8.353%	$169.3016	$169.30	$169.30	$169.30
Purchase #5	$193.70	7.466%	$208.1616	$208.16	$208.15	$208.20
Purchase #6	$250.82	13.657%	$285.0745	$285.07	$285.05	$285.10
Purchase #7	$17.31	13.242%	$19.6022	$19.60	$19.60	$19.60
7 purchase totals =	$1,141.40		$1,256.5773	$1,256.57	$1,256.55	$1,256.60