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	$82.89	8.459%	$89.9017	$89.90	$89.90	$89.90
Purchase #2	$35.49	11.322%	$39.5082	$39.51	$39.50	$39.50
Purchase #3	$129.50	8.864%	$140.9789	$140.98	$141.00	$141.00
Purchase #4	$115.88	3.453%	$119.8813	$119.88	$119.90	$119.90
Purchase #5	$21.88	4.468%	$22.8576	$22.86	$22.85	$22.90
Purchase #6	$75.31	3.198%	$77.7184	$77.72	$77.70	$77.70
Purchase #7	$104.72	9.799%	$114.9815	$114.98	$115.00	$115.00
7 purchase totals =	$565.67		$605.8276	$605.83	$605.85	$605.90