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	$82.71	7.581%	$88.9802	$88.98	$89.00	$89.00
Purchase #2	$33.54	13.618%	$38.1075	$38.11	$38.10	$38.10
Purchase #3	$103.36	5.361%	$108.9011	$108.90	$108.90	$108.90
Purchase #4	$110.34	7.506%	$118.6221	$118.62	$118.60	$118.60
Purchase #5	$101.55	10.179%	$111.8868	$111.89	$111.90	$111.90
Purchase #6	$122.73	12.168%	$137.6638	$137.66	$137.65	$137.70
Purchase #7	$114.34	8.753%	$124.3482	$124.35	$124.35	$124.30
7 purchase totals =	$668.57		$728.5097	$728.51	$728.50	$728.50