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	$78.74	13.319%	$89.2274	$89.23	$89.25	$89.20
Purchase #2	$64.98	11.334%	$72.3448	$72.34	$72.35	$72.30
Purchase #3	$47.73	8.578%	$51.8243	$51.82	$51.80	$51.80
Purchase #4	$83.30	10.724%	$92.2331	$92.23	$92.25	$92.20
Purchase #5	$193.60	6.642%	$206.4589	$206.46	$206.45	$206.50
Purchase #6	$7.83	3.405%	$8.0966	$8.10	$8.10	$8.10
Purchase #7	$27.83	3.864%	$28.9054	$28.91	$28.90	$28.90
7 purchase totals =	$504.01		$549.0905	$549.09	$549.10	$549.00