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	$165.94	10.491%	$183.3488	$183.35	$183.35	$183.30
Purchase #2	$102.87	6.808%	$109.8734	$109.87	$109.85	$109.90
Purchase #3	$173.48	5.741%	$183.4395	$183.44	$183.45	$183.40
Purchase #4	$203.92	5.481%	$215.0969	$215.10	$215.10	$215.10
Purchase #5	$76.39	3.266%	$78.8849	$78.88	$78.90	$78.90
Purchase #6	$108.56	4.539%	$113.4875	$113.49	$113.50	$113.50
Purchase #7	$80.80	10.765%	$89.4981	$89.50	$89.50	$89.50
7 purchase totals =	$911.96		$973.6291	$973.63	$973.65	$973.60