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	$203.55	12.272%	$228.5297	$228.53	$228.55	$228.50
Purchase #2	$85.93	4.632%	$89.9103	$89.91	$89.90	$89.90
Purchase #3	$23.56	9.566%	$25.8137	$25.81	$25.80	$25.80
Purchase #4	$102.64	13.307%	$116.2983	$116.30	$116.30	$116.30
Purchase #5	$163.67	5.180%	$172.1481	$172.15	$172.15	$172.10
Purchase #6	$9.37	13.553%	$10.6399	$10.64	$10.65	$10.60
Purchase #7	$181.99	5.211%	$191.4735	$191.47	$191.45	$191.50
7 purchase totals =	$770.71		$834.8135	$834.81	$834.80	$834.70