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	$245.27	9.606%	$268.8306	$268.83	$268.85	$268.80
Purchase #2	$195.70	7.502%	$210.3814	$210.38	$210.40	$210.40
Purchase #3	$82.65	9.839%	$90.7819	$90.78	$90.80	$90.80
Purchase #4	$166.39	10.766%	$184.3035	$184.30	$184.30	$184.30
Purchase #5	$171.52	11.312%	$190.9223	$190.92	$190.90	$190.90
Purchase #6	$219.95	6.543%	$234.3413	$234.34	$234.35	$234.30
Purchase #7	$149.90	11.139%	$166.5974	$166.60	$166.60	$166.60
7 purchase totals =	$1,231.38		$1,346.1584	$1,346.15	$1,346.20	$1,346.10