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	$171.60	8.758%	$186.6287	$186.63	$186.65	$186.60
Purchase #2	$64.55	3.474%	$66.7925	$66.79	$66.80	$66.80
Purchase #3	$67.78	7.575%	$72.9143	$72.91	$72.90	$72.90
Purchase #4	$90.28	13.130%	$102.1338	$102.13	$102.15	$102.10
Purchase #5	$23.84	3.271%	$24.6198	$24.62	$24.60	$24.60
Purchase #6	$46.33	7.694%	$49.8946	$49.89	$49.90	$49.90
Purchase #7	$52.37	6.751%	$55.9055	$55.91	$55.90	$55.90
7 purchase totals =	$516.75		$558.8892	$558.88	$558.90	$558.80