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	$188.92	12.676%	$212.8675	$212.87	$212.85	$212.90
Purchase #2	$224.63	8.273%	$243.2136	$243.21	$243.20	$243.20
Purchase #3	$112.29	7.283%	$120.4681	$120.47	$120.45	$120.50
Purchase #4	$52.90	7.395%	$56.812	$56.81	$56.80	$56.80
Purchase #5	$81.93	10.489%	$90.5236	$90.52	$90.50	$90.50
Purchase #6	$102.32	12.288%	$114.8931	$114.89	$114.90	$114.90
Purchase #7	$107.54	4.599%	$112.4858	$112.49	$112.50	$112.50
7 purchase totals =	$870.53		$951.2637	$951.26	$951.20	$951.30