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	$71.40	4.304%	$74.4731	$74.47	$74.45	$74.50
Purchase #2	$136.34	10.661%	$150.8752	$150.88	$150.90	$150.90
Purchase #3	$148.85	11.374%	$165.7802	$165.78	$165.80	$165.80
Purchase #4	$77.62	3.490%	$80.3289	$80.33	$80.35	$80.30
Purchase #5	$173.94	4.293%	$181.4072	$181.41	$181.40	$181.40
Purchase #6	$72.58	7.792%	$78.2354	$78.24	$78.25	$78.20
Purchase #7	$95.36	10.751%	$105.6122	$105.61	$105.60	$105.60
7 purchase totals =	$776.09		$836.7122	$836.72	$836.75	$836.70