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	$147.38	12.834%	$166.2947	$166.29	$166.30	$166.30
Purchase #2	$99.73	12.591%	$112.287	$112.29	$112.30	$112.30
Purchase #3	$62.80	13.768%	$71.4463	$71.45	$71.45	$71.40
Purchase #4	$59.68	5.301%	$62.8436	$62.84	$62.85	$62.80
Purchase #5	$68.38	11.307%	$76.1117	$76.11	$76.10	$76.10
Purchase #6	$203.32	8.146%	$219.8824	$219.88	$219.90	$219.90
Purchase #7	$217.94	9.444%	$238.5223	$238.52	$238.50	$238.50
7 purchase totals =	$859.23		$947.3880	$947.38	$947.40	$947.30