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	$159.51	11.796%	$178.3258	$178.33	$178.35	$178.30
Purchase #2	$245.89	5.849%	$260.2721	$260.27	$260.25	$260.30
Purchase #3	$139.94	10.341%	$154.4112	$154.41	$154.40	$154.40
Purchase #4	$35.76	13.819%	$40.7017	$40.70	$40.70	$40.70
Purchase #5	$175.45	11.851%	$196.2426	$196.24	$196.25	$196.20
Purchase #6	$175.38	13.656%	$199.3299	$199.33	$199.35	$199.30
Purchase #7	$162.54	13.259%	$184.0912	$184.09	$184.10	$184.10
7 purchase totals =	$1,094.47		$1,213.3745	$1,213.37	$1,213.40	$1,213.30