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	$205.47	8.168%	$222.2528	$222.25	$222.25	$222.30
Purchase #2	$154.44	6.322%	$164.2037	$164.20	$164.20	$164.20
Purchase #3	$180.77	13.260%	$204.7401	$204.74	$204.75	$204.70
Purchase #4	$149.72	12.796%	$168.8782	$168.88	$168.90	$168.90
Purchase #5	$95.87	4.161%	$99.8592	$99.86	$99.85	$99.90
Purchase #6	$72.41	10.522%	$80.029	$80.03	$80.05	$80.00
Purchase #7	$127.30	8.647%	$138.3076	$138.31	$138.30	$138.30
7 purchase totals =	$985.98		$1,078.2706	$1,078.27	$1,078.30	$1,078.30