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	$247.41	10.373%	$273.0738	$273.07	$273.05	$273.10
Purchase #2	$220.52	8.631%	$239.5531	$239.55	$239.55	$239.60
Purchase #3	$111.39	10.739%	$123.3522	$123.35	$123.35	$123.40
Purchase #4	$111.61	12.131%	$125.1494	$125.15	$125.15	$125.10
Purchase #5	$225.52	11.268%	$250.9316	$250.93	$250.95	$250.90
Purchase #6	$82.50	9.538%	$90.3689	$90.37	$90.35	$90.40
Purchase #7	$48.67	9.740%	$53.4105	$53.41	$53.40	$53.40
7 purchase totals =	$1,047.62		$1,155.8395	$1,155.83	$1,155.80	$1,155.90