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	$86.93	12.266%	$97.5928	$97.59	$97.60	$97.60
Purchase #2	$117.98	10.473%	$130.336	$130.34	$130.35	$130.30
Purchase #3	$102.33	9.631%	$112.1854	$112.19	$112.20	$112.20
Purchase #4	$175.85	11.806%	$196.6109	$196.61	$196.60	$196.60
Purchase #5	$93.99	5.533%	$99.1905	$99.19	$99.20	$99.20
Purchase #6	$42.38	7.782%	$45.678	$45.68	$45.70	$45.70
Purchase #7	$12.73	4.418%	$13.2924	$13.29	$13.30	$13.30
7 purchase totals =	$632.19		$694.8860	$694.89	$694.95	$694.90