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	$75.69	4.205%	$78.8728	$78.87	$78.85	$78.90
Purchase #2	$49.50	7.581%	$53.2526	$53.25	$53.25	$53.30
Purchase #3	$87.59	4.546%	$91.5718	$91.57	$91.55	$91.60
Purchase #4	$109.36	12.775%	$123.3307	$123.33	$123.35	$123.30
Purchase #5	$133.28	3.585%	$138.0581	$138.06	$138.05	$138.10
Purchase #6	$226.67	6.399%	$241.1746	$241.17	$241.15	$241.20
Purchase #7	$158.85	9.675%	$174.2187	$174.22	$174.20	$174.20
7 purchase totals =	$840.94		$900.4793	$900.47	$900.40	$900.60