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	$65.59	7.871%	$70.7526	$70.75	$70.75	$70.80
Purchase #2	$85.31	6.301%	$90.6854	$90.69	$90.70	$90.70
Purchase #3	$235.33	6.433%	$250.4688	$250.47	$250.45	$250.50
Purchase #4	$200.52	5.443%	$211.4343	$211.43	$211.45	$211.40
Purchase #5	$112.75	13.630%	$128.1178	$128.12	$128.10	$128.10
Purchase #6	$24.54	11.324%	$27.3189	$27.32	$27.30	$27.30
Purchase #7	$43.26	3.313%	$44.6932	$44.69	$44.70	$44.70
7 purchase totals =	$767.30		$823.4710	$823.47	$823.45	$823.50