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	$131.99	12.410%	$148.37	$148.37	$148.35	$148.40
Purchase #2	$58.30	3.549%	$60.3691	$60.37	$60.35	$60.40
Purchase #3	$62.50	5.226%	$65.7663	$65.77	$65.75	$65.80
Purchase #4	$177.97	5.143%	$187.123	$187.12	$187.10	$187.10
Purchase #5	$177.96	6.496%	$189.5203	$189.52	$189.50	$189.50
Purchase #6	$72.30	11.499%	$80.6138	$80.61	$80.60	$80.60
Purchase #7	$109.46	12.722%	$123.3855	$123.39	$123.40	$123.40
7 purchase totals =	$790.48		$855.1480	$855.15	$855.05	$855.20