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	$19.52	4.822%	$20.4613	$20.46	$20.45	$20.50
Purchase #2	$79.66	7.250%	$85.4354	$85.44	$85.45	$85.40
Purchase #3	$207.38	3.790%	$215.2397	$215.24	$215.25	$215.20
Purchase #4	$141.65	3.490%	$146.5936	$146.59	$146.60	$146.60
Purchase #5	$220.91	4.624%	$231.1249	$231.12	$231.10	$231.10
Purchase #6	$54.82	7.616%	$58.9951	$59.00	$59.00	$59.00
Purchase #7	$103.52	7.126%	$110.8968	$110.90	$110.90	$110.90
7 purchase totals =	$827.46		$868.7468	$868.75	$868.75	$868.70