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	$34.75	6.753%	$37.0967	$37.10	$37.10	$37.10
Purchase #2	$187.28	7.176%	$200.7192	$200.72	$200.70	$200.70
Purchase #3	$116.36	12.542%	$130.9539	$130.95	$130.95	$131.00
Purchase #4	$167.90	6.440%	$178.7128	$178.71	$178.70	$178.70
Purchase #5	$55.87	5.753%	$59.0842	$59.08	$59.10	$59.10
Purchase #6	$163.76	12.228%	$183.7846	$183.78	$183.80	$183.80
Purchase #7	$60.64	10.439%	$66.9702	$66.97	$66.95	$67.00
7 purchase totals =	$786.56		$857.3216	$857.31	$857.30	$857.40