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	$173.82	6.642%	$185.3651	$185.37	$185.35	$185.40
Purchase #2	$69.43	10.247%	$76.5445	$76.54	$76.55	$76.50
Purchase #3	$27.58	10.410%	$30.4511	$30.45	$30.45	$30.50
Purchase #4	$31.85	6.704%	$33.9852	$33.99	$34.00	$34.00
Purchase #5	$86.67	6.394%	$92.2117	$92.21	$92.20	$92.20
Purchase #6	$83.47	7.159%	$89.4456	$89.45	$89.45	$89.40
Purchase #7	$104.54	6.605%	$111.4449	$111.44	$111.45	$111.40
7 purchase totals =	$577.36		$619.4481	$619.45	$619.45	$619.40