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	$233.34	9.206%	$254.8213	$254.82	$254.80	$254.80
Purchase #2	$154.52	6.706%	$164.8821	$164.88	$164.90	$164.90
Purchase #3	$74.54	9.621%	$81.7115	$81.71	$81.70	$81.70
Purchase #4	$94.41	7.143%	$101.1537	$101.15	$101.15	$101.20
Purchase #5	$36.81	10.844%	$40.8017	$40.80	$40.80	$40.80
Purchase #6	$52.26	7.810%	$56.3415	$56.34	$56.35	$56.30
Purchase #7	$55.37	6.783%	$59.1257	$59.13	$59.15	$59.10
7 purchase totals =	$701.25		$758.8375	$758.83	$758.85	$758.80