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	$111.78	5.488%	$117.9145	$117.91	$117.90	$117.90
Purchase #2	$130.54	4.472%	$136.3777	$136.38	$136.40	$136.40
Purchase #3	$211.48	4.682%	$221.3815	$221.38	$221.40	$221.40
Purchase #4	$81.77	10.528%	$90.3787	$90.38	$90.40	$90.40
Purchase #5	$183.84	9.413%	$201.1449	$201.14	$201.15	$201.10
Purchase #6	$181.45	4.543%	$189.6933	$189.69	$189.70	$189.70
Purchase #7	$132.39	5.627%	$139.8396	$139.84	$139.85	$139.80
7 purchase totals =	$1,033.25		$1,096.7302	$1,096.72	$1,096.80	$1,096.70