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	$113.93	13.200%	$128.9688	$128.97	$128.95	$129.00
Purchase #2	$139.95	6.662%	$149.2735	$149.27	$149.25	$149.30
Purchase #3	$114.64	10.692%	$126.8973	$126.90	$126.90	$126.90
Purchase #4	$82.81	8.215%	$89.6128	$89.61	$89.60	$89.60
Purchase #5	$138.72	5.179%	$145.9043	$145.90	$145.90	$145.90
Purchase #6	$182.89	7.625%	$196.8354	$196.84	$196.85	$196.80
Purchase #7	$101.73	7.847%	$109.7128	$109.71	$109.70	$109.70
7 purchase totals =	$874.67		$947.2049	$947.20	$947.15	$947.20