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	$50.91	12.677%	$57.3639	$57.36	$57.35	$57.40
Purchase #2	$49.36	11.811%	$55.1899	$55.19	$55.20	$55.20
Purchase #3	$124.52	5.379%	$131.2179	$131.22	$131.20	$131.20
Purchase #4	$182.67	4.174%	$190.2946	$190.29	$190.30	$190.30
Purchase #5	$51.92	5.143%	$54.5902	$54.59	$54.60	$54.60
Purchase #6	$213.81	8.397%	$231.7636	$231.76	$231.75	$231.80
Purchase #7	$109.70	4.487%	$114.6222	$114.62	$114.60	$114.60
7 purchase totals =	$782.89		$835.0423	$835.03	$835.00	$835.10