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	$35.72	7.440%	$38.3776	$38.38	$38.40	$38.40
Purchase #2	$106.36	5.824%	$112.5544	$112.55	$112.55	$112.60
Purchase #3	$171.61	8.849%	$186.7958	$186.80	$186.80	$186.80
Purchase #4	$233.94	3.617%	$242.4016	$242.40	$242.40	$242.40
Purchase #5	$152.88	4.203%	$159.3055	$159.31	$159.30	$159.30
Purchase #6	$64.94	11.365%	$72.3204	$72.32	$72.30	$72.30
Purchase #7	$107.69	12.269%	$120.9025	$120.90	$120.90	$120.90
7 purchase totals =	$873.14		$932.6578	$932.66	$932.65	$932.70