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	$160.35	6.352%	$170.5354	$170.54	$170.55	$170.50
Purchase #2	$59.56	11.469%	$66.3909	$66.39	$66.40	$66.40
Purchase #3	$57.77	3.164%	$59.5978	$59.60	$59.60	$59.60
Purchase #4	$16.78	12.629%	$18.8991	$18.90	$18.90	$18.90
Purchase #5	$189.36	9.757%	$207.8359	$207.84	$207.85	$207.80
Purchase #6	$245.86	7.754%	$264.924	$264.92	$264.90	$264.90
Purchase #7	$92.48	4.693%	$96.8201	$96.82	$96.80	$96.80
7 purchase totals =	$822.16		$885.0032	$885.01	$885.00	$884.90