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	$75.98	9.385%	$83.1107	$83.11	$83.10	$83.10
Purchase #2	$242.54	13.672%	$275.7001	$275.70	$275.70	$275.70
Purchase #3	$71.44	9.678%	$78.354	$78.35	$78.35	$78.40
Purchase #4	$172.65	7.571%	$185.7213	$185.72	$185.70	$185.70
Purchase #5	$63.72	6.788%	$68.0453	$68.05	$68.05	$68.00
Purchase #6	$90.57	13.856%	$103.1194	$103.12	$103.10	$103.10
Purchase #7	$159.66	3.112%	$164.6286	$164.63	$164.65	$164.60
7 purchase totals =	$876.56		$958.6794	$958.68	$958.65	$958.60