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	$66.45	3.503%	$68.7777	$68.78	$68.80	$68.80
Purchase #2	$206.90	6.712%	$220.7871	$220.79	$220.80	$220.80
Purchase #3	$165.88	9.287%	$181.2853	$181.29	$181.30	$181.30
Purchase #4	$142.27	4.377%	$148.4972	$148.50	$148.50	$148.50
Purchase #5	$186.80	7.271%	$200.3822	$200.38	$200.40	$200.40
Purchase #6	$90.38	8.645%	$98.1934	$98.19	$98.20	$98.20
Purchase #7	$141.70	6.412%	$150.7858	$150.79	$150.80	$150.80
7 purchase totals =	$1,000.38		$1,068.7087	$1,068.72	$1,068.80	$1,068.80