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	$71.27	9.619%	$78.1255	$78.13	$78.15	$78.10
Purchase #2	$128.64	12.514%	$144.738	$144.74	$144.75	$144.70
Purchase #3	$7.36	12.442%	$8.2757	$8.28	$8.30	$8.30
Purchase #4	$95.85	6.828%	$102.3946	$102.39	$102.40	$102.40
Purchase #5	$211.34	4.753%	$221.385	$221.39	$221.40	$221.40
Purchase #6	$51.82	10.538%	$57.2808	$57.28	$57.30	$57.30
Purchase #7	$35.58	8.713%	$38.6801	$38.68	$38.70	$38.70
7 purchase totals =	$601.86		$650.8797	$650.89	$651.00	$650.90