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	$29.85	5.540%	$31.5037	$31.50	$31.50	$31.50
Purchase #2	$87.93	6.400%	$93.5575	$93.56	$93.55	$93.60
Purchase #3	$176.96	6.554%	$188.558	$188.56	$188.55	$188.60
Purchase #4	$53.85	3.861%	$55.9291	$55.93	$55.95	$55.90
Purchase #5	$185.86	11.805%	$207.8008	$207.80	$207.80	$207.80
Purchase #6	$38.90	12.406%	$43.7259	$43.73	$43.75	$43.70
Purchase #7	$133.30	4.591%	$139.4198	$139.42	$139.40	$139.40
7 purchase totals =	$706.65		$760.4948	$760.50	$760.50	$760.50