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	$123.41	4.175%	$128.5624	$128.56	$128.55	$128.60
Purchase #2	$93.49	3.598%	$96.8538	$96.85	$96.85	$96.90
Purchase #3	$73.45	10.810%	$81.3899	$81.39	$81.40	$81.40
Purchase #4	$37.54	7.725%	$40.44	$40.44	$40.45	$40.40
Purchase #5	$104.63	7.277%	$112.2439	$112.24	$112.25	$112.20
Purchase #6	$179.61	3.860%	$186.5429	$186.54	$186.55	$186.50
Purchase #7	$105.66	8.676%	$114.8271	$114.83	$114.85	$114.80
7 purchase totals =	$717.79		$760.8600	$760.85	$760.90	$760.80