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	$169.65	12.319%	$190.5492	$190.55	$190.55	$190.50
Purchase #2	$101.92	9.748%	$111.8552	$111.86	$111.85	$111.90
Purchase #3	$102.91	9.593%	$112.7822	$112.78	$112.80	$112.80
Purchase #4	$217.79	4.688%	$228	$228.00	$228.00	$228.00
Purchase #5	$179.56	4.656%	$187.9203	$187.92	$187.90	$187.90
Purchase #6	$163.27	13.252%	$184.9065	$184.91	$184.90	$184.90
Purchase #7	$68.78	9.818%	$75.5328	$75.53	$75.55	$75.50
7 purchase totals =	$1,003.88		$1,091.5462	$1,091.55	$1,091.55	$1,091.50