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	$80.72	11.839%	$90.2764	$90.28	$90.30	$90.30
Purchase #2	$186.60	9.445%	$204.2244	$204.22	$204.20	$204.20
Purchase #3	$236.70	8.171%	$256.0408	$256.04	$256.05	$256.00
Purchase #4	$58.35	7.788%	$62.8943	$62.89	$62.90	$62.90
Purchase #5	$80.55	4.165%	$83.9049	$83.90	$83.90	$83.90
Purchase #6	$160.58	4.258%	$167.4175	$167.42	$167.40	$167.40
Purchase #7	$33.84	4.641%	$35.4105	$35.41	$35.40	$35.40
7 purchase totals =	$837.34		$900.1688	$900.16	$900.15	$900.10