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	$41.38	3.294%	$42.7431	$42.74	$42.75	$42.70
Purchase #2	$127.86	11.799%	$142.9462	$142.95	$142.95	$142.90
Purchase #3	$122.94	6.847%	$131.3577	$131.36	$131.35	$131.40
Purchase #4	$13.92	5.671%	$14.7094	$14.71	$14.70	$14.70
Purchase #5	$133.46	10.345%	$147.2664	$147.27	$147.25	$147.30
Purchase #6	$133.42	10.371%	$147.257	$147.26	$147.25	$147.30
Purchase #7	$95.67	9.342%	$104.6075	$104.61	$104.60	$104.60
7 purchase totals =	$668.65		$730.8873	$730.90	$730.85	$730.90