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	$163.78	12.433%	$184.1428	$184.14	$184.15	$184.10
Purchase #2	$248.85	12.780%	$280.653	$280.65	$280.65	$280.70
Purchase #3	$64.89	8.666%	$70.5134	$70.51	$70.50	$70.50
Purchase #4	$211.51	7.287%	$226.9227	$226.92	$226.90	$226.90
Purchase #5	$181.74	13.645%	$206.5384	$206.54	$206.55	$206.50
Purchase #6	$178.94	12.259%	$200.8763	$200.88	$200.90	$200.90
Purchase #7	$11.57	5.276%	$12.1804	$12.18	$12.20	$12.20
7 purchase totals =	$1,061.28		$1,181.8270	$1,181.82	$1,181.85	$1,181.80