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	$16.89	8.632%	$18.3479	$18.35	$18.35	$18.30
Purchase #2	$28.28	4.572%	$29.573	$29.57	$29.55	$29.60
Purchase #3	$39.88	8.457%	$43.2527	$43.25	$43.25	$43.30
Purchase #4	$160.47	8.652%	$174.3539	$174.35	$174.35	$174.40
Purchase #5	$80.71	5.850%	$85.4315	$85.43	$85.45	$85.40
Purchase #6	$185.31	6.201%	$196.8011	$196.80	$196.80	$196.80
Purchase #7	$238.45	9.459%	$261.005	$261.01	$261.00	$261.00
7 purchase totals =	$749.99		$808.7651	$808.76	$808.75	$808.80