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	$235.51	12.392%	$264.6944	$264.69	$264.70	$264.70
Purchase #2	$185.35	8.253%	$200.6469	$200.65	$200.65	$200.60
Purchase #3	$201.59	9.290%	$220.3177	$220.32	$220.30	$220.30
Purchase #4	$78.27	6.593%	$83.4303	$83.43	$83.45	$83.40
Purchase #5	$217.30	12.637%	$244.7602	$244.76	$244.75	$244.80
Purchase #6	$177.78	11.531%	$198.2798	$198.28	$198.30	$198.30
Purchase #7	$43.92	4.504%	$45.8982	$45.90	$45.90	$45.90
7 purchase totals =	$1,139.72		$1,258.0275	$1,258.03	$1,258.05	$1,258.00