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	$126.30	5.126%	$132.7741	$132.77	$132.75	$132.80
Purchase #2	$61.56	9.604%	$67.4722	$67.47	$67.45	$67.50
Purchase #3	$250.75	13.765%	$285.2657	$285.27	$285.25	$285.30
Purchase #4	$250.99	7.522%	$269.8695	$269.87	$269.85	$269.90
Purchase #5	$6.75	12.375%	$7.5853	$7.59	$7.60	$7.60
Purchase #6	$143.86	6.584%	$153.3317	$153.33	$153.35	$153.30
Purchase #7	$232.62	13.250%	$263.4422	$263.44	$263.45	$263.40
7 purchase totals =	$1,072.83		$1,179.7407	$1,179.74	$1,179.70	$1,179.80