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	$239.77	6.410%	$255.1393	$255.14	$255.15	$255.10
Purchase #2	$9.64	4.561%	$10.0797	$10.08	$10.10	$10.10
Purchase #3	$78.33	8.403%	$84.9121	$84.91	$84.90	$84.90
Purchase #4	$159.81	7.302%	$171.4793	$171.48	$171.50	$171.50
Purchase #5	$110.40	8.506%	$119.7906	$119.79	$119.80	$119.80
Purchase #6	$60.69	10.151%	$66.8506	$66.85	$66.85	$66.90
Purchase #7	$66.37	9.163%	$72.4515	$72.45	$72.45	$72.50
7 purchase totals =	$725.01		$780.7031	$780.70	$780.75	$780.80