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	$137.85	7.244%	$147.8359	$147.84	$147.85	$147.80
Purchase #2	$225.43	9.293%	$246.3792	$246.38	$246.40	$246.40
Purchase #3	$123.86	13.739%	$140.8771	$140.88	$140.90	$140.90
Purchase #4	$32.35	10.532%	$35.7571	$35.76	$35.75	$35.80
Purchase #5	$225.31	7.803%	$242.8909	$242.89	$242.90	$242.90
Purchase #6	$53.34	11.300%	$59.3674	$59.37	$59.35	$59.40
Purchase #7	$172.57	12.738%	$194.552	$194.55	$194.55	$194.60
7 purchase totals =	$970.71		$1,067.6596	$1,067.67	$1,067.70	$1,067.80