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	$86.43	3.270%	$89.2563	$89.26	$89.25	$89.30
Purchase #2	$242.30	6.186%	$257.2887	$257.29	$257.30	$257.30
Purchase #3	$234.59	10.488%	$259.1938	$259.19	$259.20	$259.20
Purchase #4	$221.93	5.854%	$234.9218	$234.92	$234.90	$234.90
Purchase #5	$244.36	6.452%	$260.1261	$260.13	$260.15	$260.10
Purchase #6	$35.68	6.797%	$38.1052	$38.11	$38.10	$38.10
Purchase #7	$85.82	4.850%	$89.9823	$89.98	$90.00	$90.00
7 purchase totals =	$1,151.11		$1,228.8742	$1,228.88	$1,228.90	$1,228.90