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	$82.53	8.839%	$89.8248	$89.82	$89.80	$89.80
Purchase #2	$82.44	7.867%	$88.9256	$88.93	$88.95	$88.90
Purchase #3	$75.98	7.343%	$81.5592	$81.56	$81.55	$81.60
Purchase #4	$223.30	10.792%	$247.3985	$247.40	$247.40	$247.40
Purchase #5	$237.78	7.590%	$255.8275	$255.83	$255.85	$255.80
Purchase #6	$185.86	13.874%	$211.6462	$211.65	$211.65	$211.60
Purchase #7	$242.51	8.425%	$262.9415	$262.94	$262.95	$262.90
7 purchase totals =	$1,130.40		$1,238.1233	$1,238.13	$1,238.15	$1,238.00