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	$98.81	3.450%	$102.2189	$102.22	$102.20	$102.20
Purchase #2	$174.66	12.377%	$196.2777	$196.28	$196.30	$196.30
Purchase #3	$148.97	4.407%	$155.5351	$155.54	$155.55	$155.50
Purchase #4	$8.32	12.688%	$9.3756	$9.38	$9.40	$9.40
Purchase #5	$141.30	10.439%	$156.0503	$156.05	$156.05	$156.10
Purchase #6	$35.27	6.332%	$37.5033	$37.50	$37.50	$37.50
Purchase #7	$84.82	6.262%	$90.1314	$90.13	$90.15	$90.10
7 purchase totals =	$692.15		$747.0923	$747.10	$747.15	$747.10