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	$222.29	4.151%	$231.5173	$231.52	$231.50	$231.50
Purchase #2	$196.78	9.392%	$215.2616	$215.26	$215.25	$215.30
Purchase #3	$174.55	7.194%	$187.1071	$187.11	$187.10	$187.10
Purchase #4	$166.26	5.860%	$176.0028	$176.00	$176.00	$176.00
Purchase #5	$80.87	10.248%	$89.1576	$89.16	$89.15	$89.20
Purchase #6	$110.46	5.568%	$116.6104	$116.61	$116.60	$116.60
Purchase #7	$30.89	13.578%	$35.0842	$35.08	$35.10	$35.10
7 purchase totals =	$982.10		$1,050.7410	$1,050.74	$1,050.70	$1,050.80