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	$236.34	13.656%	$268.6146	$268.61	$268.60	$268.60
Purchase #2	$157.78	9.787%	$173.2219	$173.22	$173.20	$173.20
Purchase #3	$169.48	5.789%	$179.2912	$179.29	$179.30	$179.30
Purchase #4	$31.73	3.442%	$32.8221	$32.82	$32.80	$32.80
Purchase #5	$53.53	4.505%	$55.9415	$55.94	$55.95	$55.90
Purchase #6	$167.81	11.333%	$186.8279	$186.83	$186.85	$186.80
Purchase #7	$133.50	7.399%	$143.3777	$143.38	$143.40	$143.40
7 purchase totals =	$950.17		$1,040.0969	$1,040.09	$1,040.10	$1,040.00