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	$28.60	10.289%	$31.5427	$31.54	$31.55	$31.50
Purchase #2	$231.79	10.403%	$255.9031	$255.90	$255.90	$255.90
Purchase #3	$77.74	4.780%	$81.456	$81.46	$81.45	$81.50
Purchase #4	$163.90	4.621%	$171.4738	$171.47	$171.45	$171.50
Purchase #5	$113.77	3.310%	$117.5358	$117.54	$117.55	$117.50
Purchase #6	$6.85	6.429%	$7.2904	$7.29	$7.30	$7.30
Purchase #7	$130.36	6.419%	$138.7278	$138.73	$138.75	$138.70
7 purchase totals =	$753.01		$803.9296	$803.93	$803.95	$803.90