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	$249.45	6.727%	$266.2305	$266.23	$266.25	$266.20
Purchase #2	$62.58	5.290%	$65.8905	$65.89	$65.90	$65.90
Purchase #3	$211.33	3.579%	$218.8935	$218.89	$218.90	$218.90
Purchase #4	$74.88	4.581%	$78.3103	$78.31	$78.30	$78.30
Purchase #5	$104.97	4.155%	$109.3315	$109.33	$109.35	$109.30
Purchase #6	$47.46	11.254%	$52.8011	$52.80	$52.80	$52.80
Purchase #7	$23.56	3.577%	$24.4027	$24.40	$24.40	$24.40
7 purchase totals =	$774.23		$815.8601	$815.85	$815.90	$815.80