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	$236.99	7.809%	$255.4965	$255.50	$255.50	$255.50
Purchase #2	$145.65	6.555%	$155.1974	$155.20	$155.20	$155.20
Purchase #3	$198.27	6.552%	$211.2607	$211.26	$211.25	$211.30
Purchase #4	$247.82	8.315%	$268.4262	$268.43	$268.45	$268.40
Purchase #5	$156.44	5.178%	$164.5405	$164.54	$164.55	$164.50
Purchase #6	$76.40	7.802%	$82.3607	$82.36	$82.35	$82.40
Purchase #7	$17.60	10.862%	$19.5117	$19.51	$19.50	$19.50
7 purchase totals =	$1,079.17		$1,156.7937	$1,156.80	$1,156.80	$1,156.80