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	$160.62	11.741%	$179.4784	$179.48	$179.50	$179.50
Purchase #2	$81.63	10.215%	$89.9685	$89.97	$89.95	$90.00
Purchase #3	$141.63	10.165%	$156.0267	$156.03	$156.05	$156.00
Purchase #4	$162.68	8.468%	$176.4557	$176.46	$176.45	$176.50
Purchase #5	$181.35	3.185%	$187.126	$187.13	$187.15	$187.10
Purchase #6	$134.60	6.437%	$143.2642	$143.26	$143.25	$143.30
Purchase #7	$53.80	13.400%	$61.0092	$61.01	$61.00	$61.00
7 purchase totals =	$916.31		$993.3287	$993.34	$993.35	$993.40