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	$209.88	13.835%	$238.9169	$238.92	$238.90	$238.90
Purchase #2	$73.84	11.716%	$82.4911	$82.49	$82.50	$82.50
Purchase #3	$232.29	12.207%	$260.6456	$260.65	$260.65	$260.60
Purchase #4	$186.25	6.429%	$198.224	$198.22	$198.20	$198.20
Purchase #5	$170.97	8.705%	$185.8529	$185.85	$185.85	$185.90
Purchase #6	$35.52	13.346%	$40.2605	$40.26	$40.25	$40.30
Purchase #7	$106.90	9.769%	$117.3431	$117.34	$117.35	$117.30
7 purchase totals =	$1,015.65		$1,123.7341	$1,123.73	$1,123.70	$1,123.70