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	$63.36	12.204%	$71.0925	$71.09	$71.10	$71.10
Purchase #2	$54.94	8.698%	$59.7187	$59.72	$59.70	$59.70
Purchase #3	$212.37	4.275%	$221.4488	$221.45	$221.45	$221.40
Purchase #4	$171.41	5.857%	$181.4495	$181.45	$181.45	$181.40
Purchase #5	$242.75	12.473%	$273.0282	$273.03	$273.05	$273.00
Purchase #6	$197.54	11.490%	$220.2373	$220.24	$220.25	$220.20
Purchase #7	$53.27	11.575%	$59.436	$59.44	$59.45	$59.40
7 purchase totals =	$995.64		$1,086.4110	$1,086.42	$1,086.45	$1,086.20