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	$100.35	12.501%	$112.8948	$112.89	$112.90	$112.90
Purchase #2	$51.75	3.292%	$53.4536	$53.45	$53.45	$53.50
Purchase #3	$164.72	5.693%	$174.0975	$174.10	$174.10	$174.10
Purchase #4	$187.42	7.259%	$201.0248	$201.02	$201.00	$201.00
Purchase #5	$10.71	11.428%	$11.9339	$11.93	$11.95	$11.90
Purchase #6	$57.45	3.192%	$59.2838	$59.28	$59.30	$59.30
Purchase #7	$165.73	9.420%	$181.3418	$181.34	$181.35	$181.30
7 purchase totals =	$738.13		$794.0302	$794.01	$794.05	$794.00